Dependencies: bump versions

* actions/setup-ruby is now deprecated. Use ruby/setup-ruby instead.
* Remove useless dependency installation step now provided by
  ruby/setup-ruby action.
* Bump actions/checkout to v4
* Build on Ubuntu 22.04
* Don't test ruby 2.6 anymore
* Add tests for ruby 3.3

.github/workflows/ruby.yml

@@ -11,55 +11,45 @@ on:
 jobs:
   rubocop:
     name: Rubocop
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
     steps:
-      - uses: actions/checkout@v1
-      - uses: actions/setup-ruby@v1
+      - uses: actions/checkout@v4
+      - uses: ruby/setup-ruby@v1
         with:
           ruby-version: 2.7
-      - name: Install dependencies
-        run: |
-          gem install bundler
-          bundler install
+          bundler-cache: true
       - name: Check code
         run: bundle exec rubocop
 
   test:
     needs: rubocop
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
     strategy:
       fail-fast: false
       matrix:
-        ruby-version: ['2.6', '2.7', '3.0', '3.1', '3.2']
+        ruby-version: ['2.7', '3.0', '3.1', '3.2', '3.3']
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - name: Set up Ruby
         uses: ruby/setup-ruby@v1
         with:
           ruby-version: ${{ matrix.ruby-version }}
           bundler-cache: true
-      - name: Install dependencies
-        run: |
-          gem install bundler
-          bundler install
       - name: Run tests
         run: bundle exec rspec
 
   publish:
     name: Build and Publish to Rubygems
     needs: test
     if: contains(github.ref, 'refs/tags/')
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-22.04
     steps:
-      - uses: actions/checkout@v1
-      - uses: actions/setup-ruby@v1
+      - uses: actions/checkout@v4
+      - uses: ruby/setup-ruby@v1
         with:
           ruby-version: 2.7
-      - name: Install dependencies
-        run: |
-          gem install bundler
-          bundler install
+          bundler-cache: true
       - name: Build
         run: gem build *.gemspec
       - name: Push on Rubygems