TST: Upload to codecov as separate job

[pllim]

Description

This pull request is to upload to codecov as separate job so it can be re-uploaded separately on upload failure without re-running test suite.

There is now a new job called CI / Upload Coverage (pull_request) in the CI checks. If upload fails, you can just rerun this one instead of the test suite with coverage again.

Also see:

• CI: failure of coverage upload doesn't change job status astropy/astropy#16379

Change log entry

• Is a change log needed? If yes, is it added to CHANGES.rst? If you want to avoid merge conflicts,
  list the proposed change log here for review and add to CHANGES.rst before merge. If no, maintainer
  should add a no-changelog-entry-needed label.

Checklist for package maintainer(s)

This checklist is meant to remind the package maintainer(s) who will review this pull request of some common things to look for. This list is not exhaustive.

• Are two approvals required? Branch protection rule does not check for the second approval. If a second approval is not necessary, please apply the trivial label.
• Do the proposed changes actually accomplish desired goals? Also manually run the affected example notebooks, if necessary.
• Do the proposed changes follow the STScI Style Guides?
• Are tests added/updated as required? If so, do they follow the STScI Style Guides?
• Are docs added/updated as required? If so, do they follow the STScI Style Guides?
• Did the CI pass? If not, are the failures related?
• Is a milestone set? Set this to bugfix milestone if this is a bug fix and needs to be released ASAP; otherwise, set this to the next major release milestone. Bugfix milestone also needs an accompanying backport label.
• After merge, any internal documentations need updating (e.g., JIRA, Innerspace)? 🐱

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.72%. Comparing base (bcea12f) to head (5272596).
Report is 8 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2865      +/-   ##
==========================================
- Coverage   88.93%   88.72%   -0.22%     
==========================================
  Files         111      111              
  Lines       17165    17101      -64     
==========================================
- Hits        15266    15173      -93     
- Misses       1899     1928      +29     

☔ View full report in Codecov by Sentry.
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[pllim]

This in the log is not our problem:

(node:1636) [DEP0005] DeprecationWarning: Buffer() is deprecated due to security and usability issues. Please use the Buffer.alloc(), Buffer.allocUnsafe(), or Buffer.from() methods instead.

actions/download-artifact#283

[rosteen]

Super useful - looks good to me, thanks!

[pllim]

Over at OpenAstronomy/github-actions-workflows#199 , I found a bug in this setup where if we have two jobs that generate coverage, one will clobber the other. Since we only have one coverage job here, it doesn't matter. But if the situation change in the future, we can either switch to OpenAstronomy or I apply the same patch here. FYI.