Test with older version of bundler

Author: etagwerker

.github/workflows/ci.yml

@@ -22,7 +22,7 @@ jobs:
         ruby-version: ${{ matrix.ruby }}
     - name: Install dependencies
       run: |
-        gem install bundler
+        gem install bundler -v=2.4.13
         bundle install --jobs 4 --retry 3
     - name: Run tests
       run: bundle exec rake