Sync eng/common directory with azure-sdk-tools for PR 1425 (#18868)

* Trim off the target branch

* Update eng/common/scripts/get-markdown-files-from-changed-files.ps1

Co-authored-by: Wes Haggard <weshaggard@users.noreply.github.com>

* Update get-markdown-files-from-changed-files.ps1

* Update get-markdown-files-from-changed-files.ps1

* Trim the slash

Co-authored-by: Sima Zhu <sizhu@microsoft.com>
Co-authored-by: Sima Zhu <48036328+sima-zhu@users.noreply.github.com>
Co-authored-by: Wes Haggard <weshaggard@users.noreply.github.com>

eng/common/scripts/get-markdown-files-from-changed-files.ps1

@@ -2,7 +2,7 @@ param (
   # The root repo we scaned with.
   [string] $RootRepo = '$PSScriptRoot/../../..',
   # The target branch to compare with.
-  [string] $targetBranch = "origin/${env:SYSTEM_PULLREQUEST_TARGETBRANCH}"
+  [string] $targetBranch = ("origin/${env:SYSTEM_PULLREQUEST_TARGETBRANCH}" -replace "/refs/heads/")
 )
 $deletedFiles = (git diff $targetBranch HEAD --name-only --diff-filter=D)
 $renamedFiles = (git diff $targetBranch HEAD --diff-filter=R)