Bump actions/checkout, julia-actions/setup-julia version

[ReubenJ]

actions/checkout@v1 was producing some warnings regarding Node versions (see: https://github.blog/changelog/2023-06-13-github-actions-all-actions-will-run-on-node16-instead-of-node12-by-default/)

Also bumped julia-actions/setup-julia from v1->v2 while I was at it.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.78%. Comparing base (cf77b53) to head (47209d0).
Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #85      +/-   ##
==========================================
- Coverage   93.46%   89.78%   -3.69%     
==========================================
  Files           7        6       -1     
  Lines         306      323      +17     
==========================================
+ Hits          286      290       +4     
- Misses         20       33      +13     

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[gdalle]

Thanks! I also bumped the codecov action and updated the Documenter script while we're at it. That would explain the code coverage hit.