Fix update by rebase being wrongly disabled by protected base branch (#22825)

The branch this is force pushing to is the head branch in the head repo,
so it should be checking if that is protected, not the base.

services/pull/update.go

@@ -106,7 +106,7 @@ func IsUserAllowedToUpdate(ctx context.Context, pull *issues_model.PullRequest,
 		BaseBranch: pull.HeadBranch,
 	}
 
-	pb, err := git_model.GetFirstMatchProtectedBranchRule(ctx, pull.BaseRepoID, pull.BaseBranch)
+	pb, err := git_model.GetFirstMatchProtectedBranchRule(ctx, pr.BaseRepoID, pr.BaseBranch)
 	if err != nil {
 		return false, false, err
 	}