Add retry to wait for branch deletion

Attemp to fix a transient failure
Signed-off-by: Nailia Iskhakova <niskhakova@gitlab.com>

qa/qa/specs/features/api/3_create/merge_request/push_options_remove_source_branch_spec.rb

@@ -38,7 +38,11 @@ module QA
         end.merge_via_api!
 
         expect(merge_request[:state]).to eq('merged')
-        expect(project).not_to have_branch(branch)
+
+        # Retry in case the branch deletion takes more time to finish
+        QA::Support::Retrier.retry_on_exception(max_attempts: 5, sleep_interval: 5) do
+          expect(project).not_to have_branch(branch)
+        end
       end
     end
   end