Outdated version of bundler

[Laguna1989]

The version of bundler used with this github action is (2.1.4). According to the bundler rubygems website this is from January 2020 and by that already four years old.

The latest version as of today is 2.5.5 from 2024-01-18.

This poses not only a big concern to supported features but can also mean a massive security risk.

I strongly advice to upgrade to the latest version as soon as possible and on a regular basis.