fix(ci): restore test qualification on current main

[deepujain]

Full CI on current main is blocked before this dependency's product changes: the test workflow references an action rejected by enterprise policy, and merged #484 changed Brev UnauthorizedError output while two existing tests still require raw 401/JSON text.

Use the enterprise-allowlisted immutable 8398a7/action-slack revision with the existing webhook and failure-only notification behavior. Update the test workflow's checkout to v4 (the existing #304 proposal) so actionlint accepts the modified workflow. Keep the same tests, coverage and artifacts. Update the stale auth assertions to verify #484's intended API-key/login guidance and absence of raw control-plane error output; production authentication code is unchanged.

Required validation dependency for SSH Include recovery #507, related to NVIDIA/NemoClaw#13090.

Evidence:

• Current-head startup failure identifies ravsamhq/notify-slack-action@v1 as forbidden by enterprise policy. Base main's test workflow also has startup failure.
• Base a0190d24655f57f327778f7708d8a6f634afdb1a legacy CI logs fail the same HTTPResponseError assertions. Equivalent local focused tests reproduce on base and pass with these assertion corrections.
• go test -race ./pkg/store -run '^TestHTTPResponseError_' -count=1, gofumpt, git diff check and actionlint of the modified workflow pass. Hosted full CI and code-owner review remain required.

[deepujain]

This prerequisite is ready for the repository's review and CI process. All eight upstream workflows are held for maintainer approval of the fork contribution; none has run yet. Please approve the runs using existing Actions write authority. I have no upstream write/approval permission.

Exact candidate 313eee680ad51929a7fce6b4dfb6f5e628b119fa against base a0190d24655f57f327778f7708d8a6f634afdb1a. Focused auth tests with the race detector, gofumpt, diff checks and actionlint pass. Required code-owner review, Copilot review policy and full upstream checks remain pending. No passing full CI is claimed.