Skip opening a PR if there are no builder updates

[pacostas]

Summary

This PR:

• skips calling the open PR step, if there are no commits on the branch
• Refactors the update builder action, in order to accept jam version. This will be helfpull in order to specify the jam version and not always using the latest one, making the workflows more stable on updates

Use Cases

Checklist

• I have viewed, signed, and submitted the Contributor License Agreement.
• I have linked issue(s) that this PR should close using keywords or the Github UI (See docs)
• I have added an integration test, if necessary.
• I have reviewed the styleguide for guidance on my code quality.
• I'm happy with the commit history on this PR (I have rebased/squashed as needed).