bump codecov/codecov-action from 2 to 4 (#7)

---
updated-dependencies:
- dependency-name: codecov/codecov-action
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/test.yml

@@ -35,7 +35,7 @@ jobs:
       run: make coverage
 
     - name: Codecov
-      uses: codecov/codecov-action@v2
+      uses: codecov/codecov-action@v4
       with:
         token: ${{ secrets.CODECOV_TOKEN }}
         file: ./cover.out