Update Codecov CI configuration

[lbianchi-lbl]

Fixes/Addresses:

Codecov upload failures

Changes proposed in this PR:

• Use dedicated dependent job for Codecov upload (so that, in case of failure, only that job needs to be restarted, as opposed to the test suite that generated the coverage report)
• Update Action to codecov/codecov-action@v4

Legal Acknowledgement

By contributing to this software project, I agree to the following terms and conditions for my contribution:

1. I agree my contributions are submitted under the copyright and license terms described in the LICENSE.md file at the top level of this directory.
2. I represent I am authorized to make the contributions and grant the license. If my employer has rights to intellectual property that includes these contributions, I represent that I have received permission to make contributions and grant the required license on behalf of that employer.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 38.74%. Comparing base (8da0631) to head (8b29a11).
Report is 20 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1229      +/-   ##
==========================================
+ Coverage   38.54%   38.74%   +0.20%     
==========================================
  Files         164      164              
  Lines       37032    37048      +16     
  Branches     6132     6153      +21     
==========================================
+ Hits        14274    14355      +81     
+ Misses      21619    21556      -63     
+ Partials     1139     1137       -2     

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