Errors during sending are not printed out

[arxeiss]

Recently we did mistake, and stored incorrect Slack Token into Github Secret, which is used in slack-github-action. But we got no error back, which left us clueless what is wrong.

I'm not talking about #473, we don't want to set errors: true. Because that would block our pipeline. It is fine that action succeed. But it would be nice to print out that error, so we have at least some feedback.

Here is our action step:

    - name: Send Slack Notification
        id: send-notification
        uses: slackapi/slack-github-action@91efab103c0de0a537f72a35f6b8cda0ee76bf0a # v2.1.1 - https://github.com/slackapi/slack-github-action/releases
        with:
          token: ${{ secrets.SLACK_BOT_TOKEN }}
          method: chat.postMessage
          payload: >-
            {
              "channel": "${{ secrets.SLACK_CHANNEL_FOR_DEPLOYMENT }}",
              "text": "*Starting new release ${{ github.event.release.tag_name }}.*"
            }

And this is what we see. No output, but no message in Slack either.