Add special main github action for codecov

.github/workflows/main.yml

@@ -0,0 +1,41 @@
+# This workflow exists solely to send the current code coverage of the `main` branch to Codecov. This is used
+# both for the README badge and for the codecov bot's comment on PRs.
+
+name: Main
+
+on:
+  push:
+    branches:
+      - main
+
+permissions:
+  contents: read
+
+env:
+  NODE_VERSION: 20.9.0
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Configure node
+        uses: actions/setup-node@v3
+        with:
+          node-version: ${{ env.NODE_VERSION }}
+
+      - name: Install packages
+        run: npm ci
+
+      - name: Lint
+        run: npm run lint
+
+      - name: Run unit tests
+        run: npm run test:ci
+
+      - name: Upload coverage reports to Codecov
+        uses: codecov/codecov-action@v3
+        env:
+          CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}