CI: Simplify ruby.yml workflow (#3159)

* build: Reformat YAML in Ruby CI Workflow

The "quoted 3.0" is about Floats in YAML risking becoming the string "3" for interpolation.

The GitHub UI for editing this file didn't like the formatting of lists in the old way, so I picked a YAML list format which also allows easy add/remove lines.

The "exclude:" directive no longer includes unused Ruby v2.4 entries.

* build: Use setup-ruby's "bundler-cache: true"

* build: Drop unused Node.js from Ruby CI Workflow

Author: olleolleolle

.github/workflows/ruby.yml

@@ -7,70 +7,42 @@ jobs:
     name: Ruby specs
     runs-on: ${{ matrix.os }}
     continue-on-error: ${{ endsWith(matrix.ruby, 'head') || matrix.ruby == 'debug' || matrix.experimental }}
-    env:
-      BUNDLE_JOBS: 4
-      BUNDLE_RETRY: 3
     strategy:
       fail-fast: false
       matrix:
         os: [ubuntu-latest]
-        node: [14]
-        ruby: [
-          2.7,
-          3.0
-        ]
-        gemfile: [
-          "gemfiles/Gemfile-rails.5.2.x",
-          "gemfiles/Gemfile-rails.6.0.x",
-          "gemfiles/Gemfile-rails.6.1.x"
-        ]
+        ruby:
+          - 2.7
+          - "3.0"
+        gemfile:
+          - gemfiles/Gemfile-rails.5.2.x
+          - gemfiles/Gemfile-rails.6.0.x
+          - gemfiles/Gemfile-rails.6.1.x
         exclude:
-          - ruby: 2.4
-            gemfile: gemfiles/Gemfile-rails.6.0.x
-          - ruby: 2.4
-            gemfile: gemfiles/Gemfile-rails.6.1.x
           - ruby: 2.5
             gemfile: gemfiles/Gemfile-rails.6.1.x
-          - ruby: 3.0
+          - ruby: "3.0"
             gemfile: gemfiles/Gemfile-rails.5.2.x
         experimental: [false]
         include:
           - ruby: 2.7
             os: ubuntu-latest
             gemfile: gemfiles/Gemfile-rails-edge
             experimental: true
-          - ruby: 3.0
+          - ruby: "3.0"
             os: ubuntu-latest
             gemfile: gemfiles/Gemfile-rails-edge
             experimental: true
 
+    env:
+      BUNDLE_GEMFILE: ${{ matrix.gemfile }}
     steps:
       - uses: actions/checkout@v2
-      - uses: actions/cache@v2
-        with:
-          path: /home/runner/bundle
-          key: bundle-use-ruby-${{ matrix.ruby }}-${{ matrix.gemfile }}-gems-${{ hashFiles(matrix.gemfile) }}-${{ hashFiles('**/*.gemspec') }}
-          restore-keys: |
-            bundle-use-ruby-${{ matrix.ruby }}-${{ matrix.gemfile }}-gems-
-
-      - name: Use Node.js ${{ matrix.node }}
-        uses: actions/setup-node@v1
-        with:
-          node-version: ${{ matrix.node }}
-
-      - name: Install yarn maybe
-        run: which yarn || npm install -g yarn
 
       - uses: ruby/setup-ruby@v1
         with:
           ruby-version: ${{ matrix.ruby }}
-
-      - name: Bundle install
-        run: |
-          gem install bundler -v 2.1.4
-          bundle config path /home/runner/bundle
-          bundle config --global gemfile ${{ matrix.gemfile }}
-          bundle install --jobs 4 --retry 3
+          bundler-cache: true # Run "bundle install", and cache the result automatically.
 
       - name: Ruby specs
-        run: bundle exec rake test
+        run: bundle exec rake