Fix origin repo check that bypasses Docker Login on PRs originating from forks.

[kzvezdarov]

PR #15708 attempts to bypass the Docker Login step in the Python tests workflow, which is currently failing on PRs originating from forks, e.g. this one #15687 . The conditional doesn't seem to work correctly as the test failures reoccur even after the fix is applied. I'm not extremely familiar with GitHub Actions, but it seems that the github.repository context variable holds the base repository name, rather than the head repository, meaning that the check always passes and docker login is always attempted.

This PR changes the comparison to be explicitly against the head repository as recorded on the pull request event - this should correctly hold the fork name, leading to a bypass of the login step for pull requests triggered by a remote fork. The changes are mostly based on looking through threads such as https://github.com/orgs/community/discussions/25217.

Closes #15725

Checklist

• This pull request references any related issue by including "closes <link to issue>"
  • If no issue exists and your change is not a small fix, please create an issue first.
• If this pull request adds new functionality, it includes unit tests that cover the changes
• If this pull request removes docs files, it includes redirect settings in mint.json.
• If this pull request adds functions or classes, it includes helpful docstrings.

[desertaxle]

Thank you!

[codspeed-hq]

CodSpeed Performance Report

Merging #15724 will not alter performance

_{Comparing kzvezdarov:fix-docker-login-on-fork (d06ab7d) with main (123f880)}

Summary

✅ 3 untouched benchmarks

[zzstoatzz]

thanks so much for the thorough write up @kzvezdarov !