github: only notify nightly E2E failures once (#5559)

.github/workflows/e2e-nightly.yml

@@ -32,14 +32,18 @@ jobs:
         working-directory: test/e2e
         run: ./run-multiple.sh networks/nightly/*-group${{ matrix.group }}-*.toml
 
+  e2e-nightly-fail:
+    needs: e2e-nightly-test
+    if: ${{ failure() }}
+    runs-on: ubuntu-latest
+    steps:
       - name: Notify Slack on failure
         uses: rtCamp/action-slack-notify@e9db0ef
-        if: ${{ failure() }}
         env:
           SLACK_WEBHOOK: ${{ secrets.SLACK_WEBHOOK }}
           SLACK_CHANNEL: tendermint-internal
-          SLACK_USERNAME: Nightly E2E Test Failure
+          SLACK_USERNAME: Nightly E2E Tests
           SLACK_ICON_EMOJI: ':skull:'
           SLACK_COLOR: danger
-          SLACK_MESSAGE: Nightly E2E test failed (group ${{ matrix.group }})
+          SLACK_MESSAGE: Nightly E2E tests failed
           SLACK_FOOTER: ''