Remove unnecessary Ruby definitions

[jenshenny]

What are you trying to accomplish?

The .ruby-version file is the ecosystem standard for defining a Ruby version. This PR removes all other references to Ruby as the tools will read from .ruby-version.

What approach did you choose and why?

• Removed Ruby version in dev.yml as dev reads from .ruby-version
• Upgraded Rubocop to 1.61+ as the TargetRubyVersion will start reading from the required_ruby_version from the gemspec
• Remove ruby version from lint and typechecking, GH actions will use the Ruby version in .ruby-version.
  • Reintroduced the bundler cache option and removed the manual install of gems for typechecking. This is done by ignoring vendored gems from the sorbet config as what sorbet does now. sorbet/sorbet@cfc7c37

Type of Change

• Bugfix
• New feature
• Non-breaking change (a change that doesn't alter functionality - i.e., code refactor, configs, etc.)

Additional Release Notes

• Breaking change (fix or feature that would cause existing functionality to change)

Include any notes here to include in the release description. For example, if you selected "breaking change" above, leave notes on how users can transition to this version.

If no additional notes are necessary, delete this section or leave it unchanged.

Checklist

• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• It is safe to rollback this change.