chore(action): Update automated-updates-to-sam-cli.yml to check if PR already exist

[roger-zhangg]

Which issue(s) does this change fix?

Why is this change necessary?

This workflow will still force push to change the commit even if the version change is already there. Causing unit test to run over and over again and therefore stopped at some point.

How does it address the issue?

This change will stop the workflow form executing if the PR already exist.

What side effects does this change have?

If a PR is updating to 1.107, and our latest version is 1.108, we need to manually close 1.107.

Mandatory Checklist

PRs will only be reviewed after checklist is complete

• Review the generative AI contribution guidelines
• Add input/output type hints to new functions/methods
• Write design document if needed (Do I need to write a design document?)
• Write/update unit tests
• Write/update integration tests
• Write/update functional tests if needed
• make pr passes
• make update-reproducible-reqs if dependencies were changed
• Write documentation

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[roger-zhangg]

Github Action outage, let's wait a bit