Add codecov workflow

Author: elgopher

.github/workflows/build.yml

@@ -22,4 +22,20 @@ jobs:
       run: go build -v ./...
 
     - name: Test
-      run: go test -v ./...
+      run: go test -race -v ./...
+
+  coverage:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+
+      - name: Set up Go
+        uses: actions/setup-go@v3
+        with:
+          go-version: 1.18
+
+      - name: Test
+        run: go test -v -coverprofile=coverage.txt -covermode=atomic ./...
+
+      - name: Upload coverage to Codecov
+        run: bash <(curl -s https://codecov.io/bash)