Run CI alert steps only on main (#797)

Part of https://www.notion.so/Alerting-for-failing-CI-jobs-d0183b65453947aeab11dbddf989d9c0

- Run CI alert steps only on main to avoid alerts for in-progress PRs
- The Slack alerts will be sent on a CI job failure if
  - A commit is pushed directly to main
  - A PR gets merged into main
  - A scheduled job runs on main

Reviewed-on: #797
Co-authored-by: Prathamesh Musale <prathamesh.musale0@gmail.com>
Co-committed-by: Prathamesh Musale <prathamesh.musale0@gmail.com>

.gitea/workflows/test-database.yml

@@ -50,7 +50,7 @@ jobs:
           join_cgroup
           ./tests/database/run-test.sh
       - name: Notify Vulcanize Slack on CI failure
-        if: always()
+        if: ${{ always() && github.ref_name == 'main' }}
         uses: ravsamhq/notify-slack-action@v2
         with:
           status: ${{ job.status }}
@@ -58,7 +58,7 @@ jobs:
         env:
           SLACK_WEBHOOK_URL: ${{ secrets.VULCANIZE_SLACK_CI_ALERTS }}
       - name: Notify DeepStack Slack on CI failure
-        if: always()
+        if: ${{ always() && github.ref_name == 'main' }}
         uses: ravsamhq/notify-slack-action@v2
         with:
           status: ${{ job.status }}