[ci] use override: post-release-<package> label (#11429)

The ci only capture label that starts with `override:`. We can either (1)  update the ci to capture more labels, or (2) update the post release label to start with `override:`.

I figured adding `override:` prefix is more appropriate because the label is attempting to override verision check for batch release.

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Author: chunhtai

.github/workflows/sync_release_pr.yml

@@ -41,4 +41,4 @@ jobs:
             --head "${{ github.ref_name }}" \
             --title "Sync ${{ github.ref_name }} to main" \
             --body "This automated PR syncs the changes from the release branch ${{ github.ref_name }} back to the main branch." \
-            --label "post-${{ github.ref_name }}"
+            --label "override: post-${{ github.ref_name }}"

script/tool/lib/src/version_check_command.dart

@@ -248,7 +248,7 @@ class VersionCheckCommand extends PackageLoopingCommand {
     // PR with post release label is going to sync changelog.md and pubspec.yaml
     // change back to main branch. Proceed with regular version check.
     final bool hasPostReleaseLabel = _prLabels.contains(
-      'post-release-${pubspec.name}',
+      'override: post-release-${pubspec.name}',
     );
     bool versionChanged;
 

script/tool/test/version_check_command_test.dart

@@ -2079,7 +2079,7 @@ release:
         },
       );
       test(
-        'ignores changelog and pubspec yaml version modifications check with post-release label',
+        'ignores changelog and pubspec yaml version modifications check with override: post-release label',
         () async {
           final RepositoryPackage package = createFakePackage(
             'package',
@@ -2112,7 +2112,7 @@ packages/package/pubspec.yaml
           final List<String> output = await runCapturingPrint(runner, <String>[
             'version-check',
             '--base-sha=main',
-            '--pr-labels=post-release-package',
+            '--pr-labels=override: post-release-package',
           ]);
 
           expect(