ci: post regression notifications if scheduled tests do not succeed (#1376)

Author: zimeg

.github/workflows/tests.yml

@@ -86,7 +86,7 @@ jobs:
     name: Regression notifications
     runs-on: ubuntu-latest
     needs: build
-    if: failure() && github.ref == 'refs/heads/main' && github.event_name != 'workflow_dispatch'
+    if: ${{ !success() && github.ref == 'refs/heads/main' && github.event_name != 'workflow_dispatch' }}
     steps:
       - name: Send notifications of failing tests
         uses: slackapi/slack-github-action@91efab103c0de0a537f72a35f6b8cda0ee76bf0a # v2.1.1