Try to use git version of test-unit-ruby-core

Author: hsbt

.github/workflows/test.yml

@@ -25,7 +25,7 @@ jobs:
       uses: ruby/setup-ruby@v1
       with:
         ruby-version: ${{ matrix.ruby }}
-    - name: Install dependencies
-      run: bundle install
+        bundler-cache: true
+        rubygems: latest
     - name: Run test
-      run: rake test
+      run: bundle exec rake test

Gemfile

@@ -7,4 +7,4 @@ gemspec
 gem "rake"
 gem "rdoc"
 gem "test-unit"
-gem "test-unit-ruby-core"
+gem "test-unit-ruby-core", git: "https://github.com/ruby/test-unit-ruby-core"