ci: configure codecov coverage

Author: codepunkt

.github/workflows/ci.yml

@@ -34,6 +34,10 @@ jobs:
       - name: Test
         run: |
           pnpm run test
+      - name: Upload coverage reports to Codecov
+        uses: codecov/codecov-action@v5
+        with:
+          token: ${{ secrets.CODECOV_TOKEN }}
       - name: Build
         run: |
           pnpm run build