[19.4] Backport of 'Skip per-ref Redis cache in protected branch push check'

What does this MR do and why?

Backport of !267313 (merged) to 19.4.

Large pushes that create or update many refs spent one Redis round trip per ref in the protected-branch access check (Gitlab::Checks::BranchCheck), because ProtectedBranch.protected? resolves through a per-ref Redis cache that misses on every new ref. A push with thousands of refs could issue tens of thousands of Redis calls and exceed the internal push timeout, failing the push (https://gitlab.com/gitlab-org/gitlab/-/issues/637905).

This makes BranchCheck match protected branches in Ruby against the preloaded all_protected_branches association (skip_cache: true) instead of the per-ref Redis cache, exactly as ProtectedTag already does. The matching result is identical; only the caching path changes.

On the default branch the change shipped behind the skip_protected_branch_push_cache feature flag (!267313 (merged)), which was rolled out to 100% on GitLab.com and validated stable, then removed in !269360 (merged). This backport combines both into a single always-on change, so no feature flag is introduced on the stable branch.

Cherry-pick was clean; no conflicts.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• This MR is backporting a bug fix, documentation update, or spec fix, previously merged in the default branch.
• The MR that fixed the bug on the default branch has been deployed to GitLab.com (not applicable for documentation or spec changes).
• The MR title is descriptive (e.g. "Backport of 'title of default branch MR'"). This is important, since the title will be copied to the patch blog post.
• Required labels have been applied to this merge request
  • severity label and bug subtype labels (if applicable)
  • If this MR fixes a bug that affects customers, the customer label has been applied.
• This MR has been approved by a maintainer (only one approval is required).
• Ensure the e2e:test-on-omnibus-ee job has succeeded, or if it has failed, investigate the failures. If you determine the failures are unrelated, you may proceed. If you need assistance investigating, request help in the #s_developer_experience Slack channel to confirm the failures are unrelated to the merge request.

Note to the merge request author and maintainer

If you have questions about the patch release process, please:

• Refer to the patch release runbook for engineers and maintainers for guidance.
• Ask questions on the #releases Slack channel (internal only).
• Once the backport has been merged, the commit changes will be automatically deployed to a release environment that can be used for manual validation. See after merging runbook for details.