update bundler version in CI workflow

Author: hmdros

.github/workflows/main.yml

@@ -19,6 +19,6 @@ jobs:
           bundler-cache: true
       - name: Build and run tests
         run: |
-          gem install bundler -v 2.4.6
+          gem install bundler -v 2.7.2
           bundle install --jobs 4 --retry 3
           bundle exec rake