Fix flaky protected branches spec form submission race

What does this MR do and why?

Fixes two flaky example blocks.

Error: undefined method `code_owner_approval_required' for nil.

Root cause: Race condition. submit_form (line 116-119) clicks "Protect" + wait_for_requests, then the test immediately reads the DB via find_by_name. wait_for_requests doesn't guarantee the create request finished/committed, so find_by_name can return nil → undefined method code_owner_approval_required for nil.

Fix: After submitting, add a Capybara UI wait for the branch to appear in the list before the DB query.

References

• Related to gitlab-org/quality/analytics/ci-health-incidents#1206 (closed)
• Related to https://gitlab.com/gitlab-org/quality/test-failure-issues/-/work_items/44329

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