[dashboard] Show release branches regardless of repo (#3093)

Fixes flutter/flutter#133622

Release branches are generic to the repos. Remove the legacy check for the specific repo, which is no longer returned.

Updated the fake data to properly reflect the expected state.

dashboard/lib/build_dashboard_page.dart

@@ -268,7 +268,7 @@ class BuildDashboardPageState extends State<BuildDashboardPage> {
             ),
           ),
           ...buildState.branches
-              .where((Branch b) => b.repository == buildState.currentRepo && b.branch != buildState.currentBranch)
+              .where((Branch b) => b.branch != buildState.currentBranch)
               .map<DropdownMenuItem<String>>((Branch b) {
             final String branchPrefix = (b.channel != 'HEAD') ? '${b.channel}: ' : '';
             return DropdownMenuItem<String>(

dashboard/lib/logic/qualified_task.dart

@@ -18,7 +18,6 @@ class StageName {
 }
 
 /// Base URLs for various endpoints that can relate to a [Task].
-const String _cirrusUrl = 'https://cirrus-ci.com/github/flutter/flutter';
 const String _luciUrl = 'https://ci.chromium.org/p/flutter';
 const String _googleTestUrl = 'https://flutter-rob.corp.google.com';
 const String _dartInternalUrl = 'https://ci.chromium.org/p/dart-internal';

dashboard/lib/service/dev_cocoon.dart

@@ -126,19 +126,20 @@ class DevelopmentCocoonService implements CocoonService {
 
   @override
   Future<CocoonResponse<List<Branch>>> fetchFlutterBranches() async {
-    final List<Branch> fakeBranches = <Branch>[];
-    for (String repo in _repos) {
-      fakeBranches.add(
-        Branch()
-          ..repository = repo
-          ..branch = defaultBranches[repo]!,
-      );
-      fakeBranches.add(
-        Branch()
-          ..repository = repo
-          ..branch = '$repo-release',
-      );
-    }
+    final List<Branch> fakeBranches = <Branch>[
+      Branch()
+        ..channel = 'HEAD'
+        ..branch = 'master',
+      Branch()
+        ..channel = 'stable'
+        ..branch = 'flutter-3.13-candidate.0',
+      Branch()
+        ..channel = 'beta'
+        ..branch = 'flutter-3.15-candidate.5',
+      Branch()
+        ..channel = 'dev'
+        ..branch = 'flutter-3.15-candidate.12',
+    ];
     return CocoonResponse<List<Branch>>.data(fakeBranches);
   }