Fix flaky protected branches code owner spec

What does this MR do?

Fixes a flaky failure in ee/spec/features/protected_branches_spec.rb.

The two "create new protected branch with code owner" tests query the database with find_by_name right after clicking Protect, using only wait_for_requests. When the create request has not committed yet, find_by_name returns nil and the test fails with:

undefined method 'code_owner_approval_required' for nil

The CE shared examples avoid this by asserting the new branch row renders before reading the database. The EE submit_form helper skipped that step. This change waits for the .ref-name row to show the branch name, so Capybara blocks until the create lands before the DB read.

Related

Incident: gitlab-org/quality/analytics/ci-health-incidents#1206 (closed)