.github: Fix the repatriation logic to deal with merged/closed PRs

[LukeShu]

Description

If there's an old PR that's already been merged, that means we should be creating a new one, rather than assuming that pushing to the branch will update the old one.

As seen on https://github.com/emissary-ingress/emissary/runs/6523998225

Testing

I used gh on the CLI to try out these commands interactively. But I noticed some minor differences in gh pr view than what we see in CI, so apparently versions are different; so who knows if this will actually work in CI?

Checklist

• I made sure to update CHANGELOG.md. - no applicable changes

  Remember, the CHANGELOG needs to mention:

  • Any new features
  • Any changes to our included version of Envoy
  • Any non-backward-compatible changes
  • Any deprecations

• This is unlikely to impact how Ambassador performs at scale.

  Remember, things that might have an impact at scale include:

  • Any significant changes in memory use that might require adjusting the memory limits
  • Any significant changes in CPU use that might require adjusting the CPU limits
  • Anything that might change how many replicas users should use
  • Changes that impact data-plane latency/scalability

• My change is adequately tested.

  Remember when considering testing:

  • Your change needs to be specifically covered by tests.
    • Tests need to cover all the states where your change is relevant: for example, if you add a behavior that can be enabled or disabled, you'll need tests that cover the enabled case and tests that cover the disabled case. It's not sufficient just to test with the behavior enabled.
  • You also need to make sure that the entire area being changed has adequate test coverage.
    • If existing tests don't actually cover the entire area being changed, add tests.
    • This applies even for aspects of the area that you're not changing – check the test coverage, and improve it if needed!
  • We should lean on the bulk of code being covered by unit tests, but...
  • ... an end-to-end test should cover the integration points

• I updated DEVELOPING.md with any any special dev tricks I had to use to work on this code efficiently. - no tricks

• The changes in this PR have been reviewed for security concerns and adherence to security best practices.

[kflynn]

Looks good! although it makes me sad that gh doesn't output the URL in a clean way.

[kflynn]

Whoops, meant to approve instead of comment.