add action

Author: stedmen

.github/workflows/ci.yml

@@ -40,4 +40,10 @@ jobs:
         run: yarn lint
 
       - name: Test
-        run: yarn test
+        run: yarn test --coverage
+
+      - name: Upload coverage reports to Codecov
+        uses: codecov/codecov-action@v5
+        with:
+          token: ${{ secrets.CODECOV_TOKEN }}
+          slug: segmentio/tsub-js