add bundler constraint to install compatible versions with ruby versions

Author: hmdros

.github/workflows/main.yml

@@ -19,6 +19,15 @@ jobs:
           bundler-cache: true
       - name: Build and run tests
         run: |
-          gem install bundler
+          RUBY_VERSION_STR="${{ matrix.ruby-version }}"
+          case "$RUBY_VERSION_STR" in
+            2.6*) BUNDLER_CONSTRAINT=">= 2, < 3" ;;
+            2.7*) BUNDLER_CONSTRAINT=">= 2, < 4" ;;
+            3.*)  BUNDLER_CONSTRAINT=">= 3, < 4" ;;
+            *)    BUNDLER_CONSTRAINT=">= 2" ;;
+          esac
+
+          gem install bundler -v "$BUNDLER_CONSTRAINT"
+          echo "Bundler installed: $(bundle -v)"
           bundle install --jobs 4 --retry 3
           bundle exec rake