CI: Upgrade the codecov action to v4 (#506)

Author: DilumAluthge

.github/workflows/ci_unit.yml

@@ -44,7 +44,7 @@ jobs:
         env:
           COMPATHELPER_RUN_INTEGRATION_TESTS: "false"
       - uses: julia-actions/julia-processcoverage@v1
-      - uses: codecov/codecov-action@v3
+      - uses: codecov/codecov-action@v4
         with:
           file: lcov.info
           token: ${{ secrets.CODECOV_TOKEN }}