Fix code coverage & update action versions

[gdalle]

Hi there!
I looked into the lack of code coverage (e.g. in this CI log), and it turns out you're using a very outdated version of the Codecov action, which severely limits your uploads.
The solution is to update the action and add a secret CODECOV_TOKEN to the repo, following the procedure I described here: https://discourse.julialang.org/t/psa-new-version-of-codecov-action-requires-additional-setup/109857.
I used the opportunity to update other action versions.

[codecov-commenter]

⚠️ Please install the to ensure uploads and comments are reliably processed by Codecov.

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.56%. Comparing base (4d4c546) to head (96bff51).

❗ Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1954      +/-   ##
==========================================
+ Coverage   71.44%   71.56%   +0.11%     
==========================================
  Files          32       32              
  Lines       13849    13849              
==========================================
+ Hits         9895     9911      +16     
+ Misses       3954     3938      -16     

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[wsmoses]

@gdalle if I gave you relevant repo/org permissions (and let me know which ones) would you be able to setup the key?

[gdalle]

Sure but it's literally a 15 second procedure and I explain it in great detail on the discourse post, so don't feel compelled to bring me along. I'd be honored though

[gdalle]

The right way is to add an organization wide secret

[gdalle]

And actually since we've seen a codecov report in the present PR, it looks like the setup already works?

[wsmoses]

Cool, okay will merge

[gdalle]

Hi Billy! It seems like this is good to go?

[wsmoses]

@gdalle this is breaking CI with say "Error: Unable to resolve action julia-actions/cache@v4, unable to find version v4" for docs, etc

I'm going to revert and let you reopen with a fix.

[gdalle]

done in #1977, sorry for the typo, it was v2 and not v4
using dependabot might help for these kinds of updates btw