ci: Update codecov-action to v4.

[nfelt14]

Proposed changes

Update the codecov-action version to v4.

Types of changes

What types of changes does your code introduce?
Put an x in the boxes that apply

• CI/CD update (an update to the CI/CD workflows, scripts, and/or configurations)

Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your code.

• I have followed the guidelines in the CONTRIBUTING document
• I have signed the CLA
• I have checked to ensure there aren't other open Pull Requests for the same update/change
• I have performed a self-review of my code
• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• Basic linting passes locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have added necessary documentation (if appropriate)
• I have updated the Changelog with a brief description of my changes

[nfelt14]

TODO:

• Squash testing commits

[nfelt14]

Blocked by codecov/codecov-action#1278

[nfelt14]

TODO:

• Squash testing commits

The merge will squash them all.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (2dd4876) to head (1b6e070).

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #140   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files          170       170           
  Lines         3804      3804           
  Branches       643       643           
=========================================
  Hits          3804      3804           

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