Fix workflow

Author: sue445

.github/workflows/build.yml

@@ -19,7 +19,6 @@ on:
 env:
   TEST_ARGS: -coverprofile coverage.out -covermode atomic
   TEST_GEM_DIR: ruby/testdata/example/
-  GO_GEM_DIR: gem/
 
 jobs:
   test:
@@ -179,8 +178,7 @@ jobs:
           ruby-version: ${{ matrix.ruby }}
           bundler-cache: true
 
-      - run: bundle exec rspec
-        working-directory: ${{ env.GO_GEM_DIR }}
+      - run: bundle exec rake go_gem:test
 
       - name: Slack Notification (not success)
         uses: act10ns/slack@v2