fix(ci): remove disallowed Slack notification

[deepujain]

The test workflow cannot start because enterprise policy rejects ravsamhq/notify-slack-action@v1. Remove the redundant Slack failure-notification step, as requested by Pratik in the Brev support thread. GitHub already reports test failures. Update checkout to v4; tests, coverage and artifacts are preserved.

This is the CI prerequisite for SSH Include recovery #507, related to NVIDIA/NemoClaw#13090. The current diff changes only .github/workflows/test.yml.

Main now includes the auth-test expectation correction through #489. This PR reuses that merged correction and removes its duplicate auth-test changes, resolving the resulting conflict.

Validation: actionlint v1.7.7 and git diff checks pass for this workflow-only candidate, based on main 19bb28aced24f1c53a9dcf3750b1bb343c6ca071. Full upstream CI and code-owner review remain required.

Evidence: #507 startup failure identifies the disallowed notification action; the earlier main test workflow has the same startup failure. The disallowed action remains in the current main workflow.

[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.

[deepujain]

Qualification update for bb410aa299efbb06f87f95fd8c536ba9f6c9341e against 19bb28aced24f1c53a9dcf3750b1bb343c6ca071: all eight upstream workflows and ten check runs are successful; GitHub reports reviewDecision APPROVED and merge state CLEAN. Thank you, Pratik, for reviewing.

Full tests, lint, and legacy tests/release cross-build passed. The cross-build used goreleaser-cross v1.24.5 at sha256:a5a915aa72e9f92acd6fe481a73fa1da1255d96f57b62678b3106a27165109ed, building Linux and Darwin amd64/arm64 successfully. Its merge-ref source d1441a1b02e142c01de46ae33b18545008573a4f has exactly this base/head as parents. Test and legacy coverage artifacts are present and inspected.

Log limitations: Codecov uploads received HTTP 429 (coverage artifacts still available); CodeQL succeeds with no new changed-code alerts but reports existing partial Go coverage (165/271 files) and deprecated v2 actions. Missing dist uploads in test jobs do not substitute for the successful release cross-build. No absent Copilot/CodeRabbit/Advisor review is claimed passing.

The Slack notification step is removed per feedback. No additional source changes or reruns were needed. This prerequisite remains open pending maintainer merge; afterward I will synchronize and requalify #507. Production QA acceptance for #13090 remains a separate pending gate.