Ensure modules are current and tidy in CI (#22546)

* Ensure modules are current and tidy in CI

Fails the build if go.mod or go.sum isn't current.

* only fail on diff

eng/.golangci.yml

@@ -1,5 +1,7 @@
 #reference https://github.com/golangci/golangci-lint#config-file for more options
 run:
+  # ensure that go.mod files are current
+  modules-download-mode: readonly
   # default is true. Enables skipping of directories:
   #   vendor$, third_party$, testdata$, examples$, Godeps$, builtin$
   skip-dirs-use-default: true

eng/pipelines/templates/steps/analyze.yml

@@ -72,6 +72,21 @@ steps:
     failOnStderr: false
     workingDirectory: $(System.DefaultWorkingDirectory)
 
+  - pwsh: |
+      $modDirs = ./eng/scripts/get_module_dirs.ps1 '${{ parameters.ServiceDirectory }}'
+      foreach ($md in $modDirs) {
+        pushd $md
+        Write-Host "##[command]Executing go mod tidy in $md"
+        go mod tidy
+        $diff = (git diff -w .)
+        Write-Host ($diff -join "`n")
+        if ($diff.Length -gt 0) {
+          exit 1
+        }
+      }
+    displayName: 'go mod tidy'
+    workingDirectory: $(System.DefaultWorkingDirectory)
+
   - pwsh: |
       $modDirs = ./eng/scripts/get_module_dirs.ps1 '${{ parameters.ServiceDirectory }}'
       foreach ($md in $modDirs) {