ci: don't use Bundler

Author: kou

.github/workflows/test.yml

@@ -34,13 +34,18 @@ jobs:
             --sync
       - name: Install dependencies
         run: |
-          bundle install
+          gem install \
+            packnga \
+            rake \
+            yard
       - name: Build gem
         run: |
-          bundle exec rake build
+          rake build
       - name: Install as gem
         run: |
-          gem install pkg/*.gem
+          gem install \
+            rubygems-requirements-system \
+            pkg/*.gem
       - name: Install additional Groonga pakcages to run tests
         if: |
           matrix.runs-on == 'ubuntu-latest'