Remove occurrences of matrix.python-version.key || in ci.yml

[Yogendra0Sharma]

Description

Kindly take a look at CONTRIBUTING.md.

Please describe the purpose of this pull request. Reference and link to any relevant issues or pull requests.

Checklist

• [#] Have you followed the guidelines in our Contributing document?
• [#] Have you checked to ensure there aren't any other open Pull Requests for the required change?
• [#] Does your submission pass pre-commit? ($ pre-commit run --all-files or $ nox -s lint)
• [#] Does your submission pass tests? ($ pytest or $ nox -s tests)
• [#] Does the documentation build with your changes? ($ cd docs; make clean; make html or $ nox -s docs)
• [#] Does your submission pass the doctests? ($ pytest --doctest-plus src/vector/ or $ nox -s doctests)

Before Merging

• [#] Summarize the commit messages into a brief review of the Pull request.
  Remove occurrences of matrix.python-version.key || in ci.yml #516

[Saransh-cpp]

Thanks for picking this up, @Yogendra0Sharma! :)