ci: remove success message from formatting check (#858)

* ci: remove success message from formatting check

The workflow succeeds giving a green check-mark next to the commit id. Perhaps writing a comment each time is redundant?

E.g.: #856

* Update spotless check workflow to handle failures

Modify condition for PR comment action to run only on failure.

Author: MartinBernstorff

.github/workflows/spotless-check.yml

@@ -20,11 +20,12 @@ jobs:
       - name: spotless:check
         run: mvn spotless:check
       -  uses: mshick/add-pr-comment@v2
-         if: always()
+         # Only run if the previous step failed
+         if: failure() && steps.spotless_check.outcome == 'failure'
          with:
            proxy-url: https://slack-bots.azure.smilecdr.com/robogary/github
            message-success: |
-             Formatting check succeeded!
+             Formatting check succeeded! This should never run, because the step is skipped on workflow success.
            message-failure: |
              **This Pull Request has failed the formatting check**