ci: Add Codecov integration for coverage reports

This commit integrates Codecov into the CI workflow. It adds a new step to upload coverage reports to Codecov after the tests have been run. This allows us to track code coverage over time and identify areas of the codebase that are not well-tested. The Codecov token is retrieved from the repository secrets.

Author: ioncakephper

.github/workflows/ci.yml

@@ -32,3 +32,9 @@ jobs:
 
       - name: Run tests
         run: npm test
+
+      - name: Upload coverage reports to Codecov
+        uses: codecov/codecov-action@v5
+        with:
+          token: ${{ secrets.CODECOV_TOKEN }}
+          slug: ioncakephper/php-theme-gen