Release v3.1.0

Add job field.
Previously, the action field could be used to get the link per workflow, but there was no link per job.
The addition of the job link indicated by that notification makes it more useful.

      - uses: 8398a7/action-slack@v3
        with:
          status: ${{ job.status }}
          fields: repo,commit,job # Choose any field you want
        env:
          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }} # required
          SLACK_WEBHOOK_URL: ${{ secrets.SLACK_WEBHOOK_ URL }}