ci: expand test coverage to Ruby 3.4 and Rails 7.2, fix RSpec hash formatting

[snaka]

Motivation / Background

This Pull Request has been created because the CI test matrix needed to be expanded to include Ruby 3.4 and Rails 7.2 support, and there was a compatibility issue with hash output formatting across different Ruby versions that was causing RSpec test failures.

Detail

This Pull Request changes:

1. CI Test Matrix Expansion: Adds Ruby 3.4 and Rails 7.2 to the GitHub Actions test matrix to ensure compatibility with newer versions
2. Ruby Version Compatibility: Fixes hash output format in RSpec matcher tests to work consistently across Ruby versions by using #inspect method instead of string interpolation
3. Rails 7.2 Support: Adds Gemfile.rails72 configuration file to support Rails 7.2 stable branch testing

[snaka]

Related to:

• Test against Rails 7.2, 8.0 and Ruby 3.4 on CI #457

[nashby]

@snaka thanks!