Confirm test target branch can be checked out

Confirm the target branch can be checked out to avoid a race condition
where the subsequent push option attempts to create an MR before the
target branch is ready.

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

@@ -25,6 +25,18 @@ module QA
           push.file_content = "Target branch test target branch #{SecureRandom.hex(8)}"
         end
 
+        # Confirm the target branch can be checked out to avoid a race condition
+        # where the subsequent push option attempts to create an MR before the target branch is ready.
+        Support::Retrier.retry_on_exception(sleep_interval: 5) do
+          Git::Repository.perform do |repository|
+            repository.uri = project.repository_http_location.uri
+            repository.use_default_credentials
+            repository.clone
+            repository.configure_identity('GitLab QA', 'root@gitlab.com')
+            repository.checkout(target_branch)
+          end
+        end
+
         Resource::Repository::ProjectPush.fabricate! do |push|
           push.project = project
           push.branch_name = "push-options-test-#{SecureRandom.hex(8)}"