Fix incorrect tailwind migration (#30007)

Fixes #30005. Regression from
#29945.

There was only once instance of `tw-content-center` before that PR, so I
just ran below command and reverted that one instance.

```sh
perl -p -i -e 's#tw-content-center#tw-items-center#g' web_src/js/**/* templates/**/* models/**/* tests/**/*
```

Author: silverwind

templates/admin/emails/list.tmpl

@@ -4,7 +4,7 @@
 			{{ctx.Locale.Tr "admin.emails.email_manage_panel"}} ({{ctx.Locale.Tr "admin.total" .Total}})
 		</h4>
 		<div class="ui attached segment">
-			<div class="ui secondary filter menu tw-content-center gt-mx-0">
+			<div class="ui secondary filter menu tw-items-center gt-mx-0">
 				<form class="ui form ignore-dirty tw-flex-1">
 					{{template "shared/search/combo" dict "Value" .Keyword}}
 				</form>

templates/admin/org/list.tmpl

@@ -7,7 +7,7 @@
 			</div>
 		</h4>
 		<div class="ui attached segment">
-			<div class="ui secondary filter menu tw-content-center gt-mx-0">
+			<div class="ui secondary filter menu tw-items-center gt-mx-0">
 				<form class="ui form ignore-dirty tw-flex-1">
 					{{template "shared/search/combo" dict "Value" .Keyword "Placeholder" (ctx.Locale.Tr "search.org_kind")}}
 				</form>

templates/admin/repo/unadopted.tmpl

@@ -20,7 +20,7 @@
 				{{if .Dirs}}
 					<div class="ui aligned divided list">
 						{{range $dirI, $dir := .Dirs}}
-							<div class="item tw-flex tw-content-center">
+							<div class="item tw-flex tw-items-center">
 								<span class="tw-flex-1"> {{svg "octicon-file-directory-fill"}} {{$dir}}</span>
 								<div>
 									<button class="ui button primary show-modal gt-p-3" data-modal="#adopt-unadopted-modal-{{$dirI}}">{{svg "octicon-plus"}} {{ctx.Locale.Tr "repo.adopt_preexisting_label"}}</button>

templates/admin/stacktrace-row.tmpl

@@ -1,5 +1,5 @@
 <div class="item">
-	<div class="tw-flex tw-content-center">
+	<div class="tw-flex tw-items-center">
 		<div class="icon gt-ml-3 gt-mr-3">
 			{{if eq .Process.Type "request"}}
 				{{svg "octicon-globe" 16}}
@@ -40,7 +40,7 @@
 						</summary>
 						<div class="list">
 							{{range .Entry}}
-								<div class="item tw-flex tw-content-center">
+								<div class="item tw-flex tw-items-center">
 									<span class="icon gt-mr-4">{{svg "octicon-dot-fill" 16}}</span>
 									<div class="content tw-flex-1">
 										<div class="header"><code>{{.Function}}</code></div>

templates/admin/stacktrace.tmpl

@@ -1,7 +1,7 @@
 {{template "admin/layout_head" (dict "ctxData" . "pageClass" "admin monitor")}}
 <div class="admin-setting-content">
 
-	<div class="tw-flex tw-content-center">
+	<div class="tw-flex tw-items-center">
 		<div class="tw-flex-1">
 			<div class="ui compact small menu">
 				<a class="{{if eq .ShowGoroutineList "process"}}active {{end}}item" href="?show=process">{{ctx.Locale.Tr "admin.monitor.process"}}</a>

templates/base/head_navbar.tmpl

@@ -56,7 +56,7 @@
 	<div class="navbar-right ui secondary menu">
 		{{if and .IsSigned .MustChangePassword}}
 			<div class="ui dropdown jump item" data-tooltip-content="{{ctx.Locale.Tr "user_profile_and_more"}}">
-				<span class="text tw-flex tw-content-center">
+				<span class="text tw-flex tw-items-center">
 					{{ctx.AvatarUtils.Avatar .SignedUser 24 "gt-mr-2"}}
 					<span class="only-mobile gt-ml-3">{{.SignedUser.Name}}</span>
 					<span class="not-mobile">{{svg "octicon-triangle-down"}}</span>
@@ -83,8 +83,8 @@
 				<span class="only-mobile gt-ml-3">{{ctx.Locale.Tr "active_stopwatch"}}</span>
 			</a>
 			<div class="active-stopwatch-popup item tippy-target gt-p-3">
-				<div class="tw-flex tw-content-center">
-					<a class="stopwatch-link tw-flex tw-content-center" href="{{.ActiveStopwatch.IssueLink}}">
+				<div class="tw-flex tw-items-center">
+					<a class="stopwatch-link tw-flex tw-items-center" href="{{.ActiveStopwatch.IssueLink}}">
 						{{svg "octicon-issue-opened" 16 "gt-mr-3"}}
 						<span class="stopwatch-issue">{{.ActiveStopwatch.RepoSlug}}#{{.ActiveStopwatch.IssueIndex}}</span>
 						<span class="ui primary label stopwatch-time gt-my-0 gt-mx-4" data-seconds="{{.ActiveStopwatch.Seconds}}">
@@ -142,7 +142,7 @@
 			</div><!-- end dropdown menu create new -->
 
 			<div class="ui dropdown jump item gt-mx-0 gt-pr-3" data-tooltip-content="{{ctx.Locale.Tr "user_profile_and_more"}}">
-				<span class="text tw-flex tw-content-center">
+				<span class="text tw-flex tw-items-center">
 					{{ctx.AvatarUtils.Avatar .SignedUser 24 "gt-mr-2"}}
 					<span class="only-mobile gt-ml-3">{{.SignedUser.Name}}</span>
 					<span class="not-mobile">{{svg "octicon-triangle-down"}}</span>

templates/explore/search.tmpl

@@ -1,4 +1,4 @@
-<div class="ui small secondary filter menu tw-content-center gt-mx-0">
+<div class="ui small secondary filter menu tw-items-center gt-mx-0">
 	<form class="ui form ignore-dirty tw-flex-1">
 		{{if .PageIsExploreUsers}}
 			{{template "shared/search/combo" dict "Value" .Keyword "Placeholder" (ctx.Locale.Tr "search.user_kind")}}

templates/explore/user_list.tmpl

@@ -1,6 +1,6 @@
 <div class="flex-list">
 	{{range .Users}}
-		<div class="flex-item tw-content-center">
+		<div class="flex-item tw-items-center">
 			<div class="flex-item-leading">
 				{{ctx.AvatarUtils.Avatar . 48}}
 			</div>

templates/org/header.tmpl

@@ -7,7 +7,7 @@
 				{{if .Org.Visibility.IsLimited}}<span class="ui large basic horizontal label">{{ctx.Locale.Tr "org.settings.visibility.limited_shortname"}}</span>{{end}}
 				{{if .Org.Visibility.IsPrivate}}<span class="ui large basic horizontal label">{{ctx.Locale.Tr "org.settings.visibility.private_shortname"}}</span>{{end}}
 			</span>
-			<span class="tw-flex tw-content-center gt-gap-2 tw-ml-auto gt-font-16 tw-whitespace-nowrap">
+			<span class="tw-flex tw-items-center gt-gap-2 tw-ml-auto gt-font-16 tw-whitespace-nowrap">
 				{{if .EnableFeed}}
 					<a class="ui basic label button gt-mr-0" href="{{.Org.HomeLink}}.rss" data-tooltip-content="{{ctx.Locale.Tr "rss_feed"}}">
 						{{svg "octicon-rss" 24}}

templates/org/home.tmpl

@@ -27,7 +27,7 @@
 				{{if .NumMembers}}
 					<h4 class="ui top attached header tw-flex">
 						<strong class="tw-flex-1">{{ctx.Locale.Tr "org.members"}}</strong>
-						<a class="text grey tw-flex tw-content-center" href="{{.OrgLink}}/members"><span>{{.NumMembers}}</span> {{svg "octicon-chevron-right"}}</a>
+						<a class="text grey tw-flex tw-items-center" href="{{.OrgLink}}/members"><span>{{.NumMembers}}</span> {{svg "octicon-chevron-right"}}</a>
 					</h4>
 					<div class="ui attached segment members">
 						{{$isMember := .IsOrganizationMember}}
@@ -41,7 +41,7 @@
 				{{if .IsOrganizationMember}}
 					<div class="ui top attached header tw-flex">
 						<strong class="tw-flex-1">{{ctx.Locale.Tr "org.teams"}}</strong>
-						<a class="text grey tw-flex tw-content-center" href="{{.OrgLink}}/teams"><span>{{.Org.NumTeams}}</span> {{svg "octicon-chevron-right"}}</a>
+						<a class="text grey tw-flex tw-items-center" href="{{.OrgLink}}/teams"><span>{{.Org.NumTeams}}</span> {{svg "octicon-chevron-right"}}</a>
 					</div>
 					<div class="ui attached table segment teams">
 						{{range .Teams}}