fix: try to vacuum non-default branches (#4911)

Whatever token we are getting does not have access to non-default
branches and generates a GitHub 403. Using the other token method seems
to work.

Author: jtmcdole

app_dart/lib/src/request_handlers/scheduler/batch_backfiller.dart

@@ -127,7 +127,9 @@ final class BatchBackfiller extends RequestHandler {
           (commit, [...tasks.map((t) => t.toRef())]),
       ], postsubmitTargets: currentTargets);
     }
-    log.debug('Built a grid of ${grid.eligibleTasks.length} target columns');
+    log.debug(
+      'Built a grid of ${grid.eligibleTasks.length} target columns for $grid',
+    );
 
     // Produce a list of tasks, ordered from highest to lowest, to backfill.
     // ... but only take the top N tasks, at most.

app_dart/lib/src/request_handlers/vacuum_github_commits.dart

@@ -83,11 +83,28 @@ final class VacuumGithubCommits extends ApiRequestHandler {
         'Listing commit for slug: $slug branch: $branch and msSinceEpoch: '
         '${queryAfter.millisecondsSinceEpoch}',
       );
-      commits = await githubService.listBranchedCommits(
-        slug,
-        branch,
-        queryAfter.millisecondsSinceEpoch,
-      );
+
+      try {
+        commits = await githubService.listBranchedCommits(
+          slug,
+          branch,
+          queryAfter.millisecondsSinceEpoch,
+        );
+      } catch (e) {
+        log.error('Failed retrieving commits from githubService', e);
+
+        final gh = config.createGitHubClientWithToken(
+          await config.githubOAuthToken,
+        );
+        commits = await gh.repositories
+            .listCommits(
+              slug,
+              sha: branch,
+              since: queryAfter,
+              until: queryBefore,
+            )
+            .toList();
+      }
       log.debug('Retrieved ${commits.length} commits from GitHub');
       // Do not try to add recent commits as they may already be processed
       // by cocoon, which can cause race conditions.
@@ -99,7 +116,7 @@ final class VacuumGithubCommits extends ApiRequestHandler {
           )
           .toList();
     } on gh.GitHubError catch (e) {
-      log.error('Failed retriving commits from GitHub', e);
+      log.error('Failed retrieving commits from GitHub', e);
     }
 
     return [