chore: prevent successful slack message from crashing the deploy job (#168364)

## Summary
We've seen it the previous 2 times that the `create-deploy-tag.yml` is
failing when it's about to send the success slack message.

Now setting that step not to break the workflow - because in fact the
tag is created and the process is running.

The reasons why the slack messaging is failing to be investigated.

.github/workflows/create-deploy-tag.yml

@@ -55,6 +55,7 @@ jobs:
       - name: Post Slack success message
         if: success()
         uses: slackapi/slack-github-action@v1.24.0
+        continue-on-error: true
         with:
           payload: |
             {