ci: checkout the actual ref instead of github's merge commit

[onerandomusername]

Github makes a merge commit for any pull requests. This checks back out our custom branch for linting and testing. This does means that we lose the benefits of being able to see what would happen if we merged with our default branch, but the problems of our custom pre-commit hooks getting different output, and different installed dependencies from what is on the branch dependending on how up-to-date our branches are, is a problem that I would rather not have.

[codecov[bot]]

Codecov Report

Merging #123 (e080ecf) into main (42e8674) will not change coverage. The diff coverage is n/a.

:exclamation: Current head e080ecf differs from pull request most recent head e90971f. Consider uploading reports for the commit e90971f to get more accurate results

@@           Coverage Diff           @@
##             main     #123   +/-   ##
=======================================
  Coverage   70.90%   70.90%           
=======================================
  Files          33       33           
  Lines        1619     1619           
  Branches      199      199           
=======================================
  Hits         1148     1148           
  Misses        439      439           
  Partials       32       32           

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[onerandomusername]

Looked a little more into this and while it does fix one issue, it causes other issues with github and actions. Not sure the best way to fix this except to just make a branch up to date with the main branch when issues occur like this...