chore(ci): upgrade slackapi/slack-github-action from v1 to v3 with breaking change fixes

[devin-ai-integration]

Upgrade slackapi/slack-github-action from v1 to v3

Dependabot opened PR #782 to bump slackapi/slack-github-action from v1 to v3, but this is a major version upgrade with breaking changes that requires configuration updates beyond just the version pin.

Breaking changes to address

The v1 → v3 upgrade requires updating the Slack notification step in .github/workflows/nightly-agent-integration.yml:

1. Authentication: v1 used the SLACK_BOT_TOKEN environment variable. v2+ requires a token input parameter instead.
2. Method input: v2+ requires a method input (e.g., method: chat.postMessage).
3. Channel specification: The channel should be specified in the payload body rather than via the channel-id input (verify v3 docs for exact behavior).
4. Remove deprecated env var: The SLACK_BOT_TOKEN env var is no longer read by v2+.
5. Node.js 24 runtime: v3 requires Node.js 24 on the GitHub Actions runner. Verify runner compatibility.

Expected updated configuration

- name: Notify Slack
  uses: slackapi/slack-github-action@v3
  with:
    method: chat.postMessage
    token: ${{ secrets.SLACK_BOT_TOKEN }}
    payload: |
      {
        "channel": "${{ secrets.SLACK_CHANNEL_ID }}",
        "text": ":red_circle: Nightly agent integration tests FAILED",
        "blocks": [
          {
            "type": "section",
            "text": {
              "type": "mrkdwn",
              "text": "*Nightly Agent CLI Integration* failed on `${{ github.ref_name }}`\n<${{ github.server_url }}/${{ github.repository }}/actions/runs/${{ github.run_id }}|View run>"
            }
          }
        ]
      }

References

• slackapi/slack-github-action v3 release notes
• v1 to v3 compare
• Dependabot PR: chore(ci): bump slackapi/slack-github-action from 1 to 3 #782
• Devin Review comment: chore(ci): bump slackapi/slack-github-action from 1 to 3 #782 (comment)