workflows: Use race detector on test

Signed-off-by: Hiroshi Hatake <[email protected]>

Author: cosmo0920

.github/workflows/ci.yaml

@@ -24,5 +24,5 @@ jobs:
         with:
           go-version: ${{ matrix.golang }}
       - name: Test
-        run: go test -v ./fluent
+        run: go test -v -race -cover -covermode=atomic ./fluent
         shell: bash