Fix incorrect divergence cache after switching default branch

Issue: After switching the default branch, other branches are still compared against the old default branch due to outdated divergence cache.

Change: Clear the divergence cache in SetRepoDefaultBranch to ensure correct comparisons against the new default branch.

Fixes #34369

Author: GWDx

services/repository/branch.go

@@ -639,6 +639,12 @@ func SetRepoDefaultBranch(ctx context.Context, repo *repo_model.Repository, newB
 		if err := actions_model.DeleteScheduleTaskByRepo(ctx, repo.ID); err != nil {
 			log.Error("DeleteCronTaskByRepo: %v", err)
 		}
+
+		// clear divergence cache
+		if err := DelRepoDivergenceFromCache(ctx, repo.ID); err != nil {
+			log.Error("DelRepoDivergenceFromCache: %v", err)
+		}
+
 		// cancel running cron jobs of this repository and delete old schedules
 		if err := actions_service.CancelPreviousJobs(
 			ctx,