CI: Simplify unstable.yml in favor of setup-ruby over manual RVM setup

Author: amatsuda

.github/workflows/unstable.yml

@@ -6,42 +6,24 @@ on:
 
 jobs:
   test:
-    runs-on: ubuntu-16.04
+    runs-on: ubuntu-latest
 
     strategy:
       matrix:
         ruby: [ruby-head, jruby-head]
 
+    env:
+      BUNDLE_WITHOUT: "benchmark"
+      JRUBY_OPTS: "--debug"
+
     steps:
       - uses: actions/checkout@v3
 
-      - name: Set up RVM
-        run: curl -sSL https://get.rvm.io | bash
-
-      - name: Set up Ruby
-        run: |
-          source $HOME/.rvm/scripts/rvm
-          rvm install ${{ matrix.ruby }} --binary --autolibs=disable
-          rvm --default use ${{ matrix.ruby }}
-
-      - name: Install java
-        run: sudo apt-get -y install openjdk-8-jre-headless
-        if: matrix.ruby == 'jruby-head'
-
-      - name: Install dependencies
-        run: |
-          source $HOME/.rvm/scripts/rvm
-          bundle config set --local without benchmark
-          bundle install --jobs=3
-
-      - name: Run tests (MRI)
-        run: |
-          source $HOME/.rvm/scripts/rvm
-          bundle exec rake
-        if: matrix.ruby == 'ruby-head'
+      - name: Setup ruby
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: ${{ matrix.ruby }}
+          bundler-cache: true # 'bundle install' and cache
 
-      - name: Run tests (JRuby)
-        run: |
-          source $HOME/.rvm/scripts/rvm
-          JRUBY_OPTS=--debug bundle exec rake
-        if: matrix.ruby == 'jruby-head'
+      - name: Run tests
+        run: bundle exec rake