Avoid defining version of bundler used for GitHub actions

Author: valscion

.github/workflows/ruby.yml

@@ -24,15 +24,12 @@ jobs:
           - rails_6_0_pundit_1
           - rails_6_0_pundit_2
         ruby-version: [ '2.6', '2.7' ]
-        bundler-version: [ '1.11' ]
         include:
           # Include Rails 6.0 / Ruby 3.0 combo
           - gemfile: rails_6_0_pundit_1
             ruby-version: '3.0'
-            bundler-version: '2.1.4'
           - gemfile: rails_6_0_pundit_2
             ruby-version: '3.0'
-            bundler-version: '2.1.4'
     continue-on-error: true
     env:
       BUNDLE_GEMFILE: gemfiles/${{ matrix.gemfile }}.gemfile
@@ -43,7 +40,6 @@ jobs:
         # change this to (see https://github.com/ruby/setup-ruby#versioning):
         uses: ruby/setup-ruby@v1
         with:
-          bundler: ${{ matrix.bundler-version }}
           ruby-version: ${{ matrix.ruby-version }}
           bundler-cache: true # runs 'bundle install' and caches installed gems automatically
       - name: Run tests