ci: upgrade Codecov action

[uniqueg]

Description

Upgrade Codecov action in GH Actions workflow to v4.

Fixes #218

Type of change

Please delete options that are not relevant.

• CI fix

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have updated the documentation (or documentation does not need to be updated)
• My changes generate no new warnings
• 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 not reduced the existing code coverage

[sourcery-ai]

Hey @uniqueg - I've reviewed your changes and they look great!

Here's what I looked at during the review

• 🟡 General issues: 1 issue found
• 🟢 Security: all looks good
• 🟢 Testing: all looks good
• 🟢 Complexity: all looks good

---

Sourcery is free for open source - if you like our reviews please consider sharing them ✨

• X
• Mastodon
• LinkedIn
• Facebook

_{Help me be more useful! Please click 👍 or 👎 on each comment to tell me if it was helpful.}

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (17bcf11) to head (e4166f1).
Report is 13 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff            @@
##               dev      #217   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           20        20           
  Lines          975       975           
=========================================
  Hits           975       975           

Flag	Coverage Δ
test_unit	100.00% <ø> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.