Bump @actions/core from 1.2.4 to 1.2.6

Bumps [@actions/core](https://github.com/actions/toolkit/tree/HEAD/packages/core) from 1.2.4 to 1.2.6.
- [Release notes](https://github.com/actions/toolkit/releases)
- [Changelog](https://github.com/actions/toolkit/blob/main/packages/core/RELEASES.md)
- [Commits](https://github.com/actions/toolkit/commits/HEAD/packages/core)

Signed-off-by: dependabot[bot] <[email protected]>

Add support for gems.rb/gems.locked

• #84

Use MSYS2's Bash instead of Git's Bash shell when using `shell: bash`

• See #64 (comment)
• Fixes #81

Update dependencies

• Update ncc (#78)
• Update the actions/cache package which can improve reliability (#79)

Add TruffleRuby 20.2.0

v1.43.0

Add TruffleRuby 20.2.0

Use $BUNDLE_GEMFILE if set to locate the Gemfile and Gemfile.lock

• #73, #74

Add JRuby 9.2.13.0

Remove lint command

* eslint has been removed.

Add support for Ruby 2.1

• Add support for Ruby 2.1 (#70, #71)

Treat error from restoring the cache as a cache miss

• Treat error from restoring the cache as a cache miss (#68, #66)
• Update README to reflect conditions for self-hosted runners (#67)
• Also include the commit in the cache key for truffleruby-head.

Add JRuby 9.2.12.0

Allow running external function before 'bundle install'

External actions may use setup-ruby, and some actions make changes/additions to the build environment. These may be needed for dependencies.

Hence, allow those external actions to run code before 'bundle install'. This is done by passing a function as a parameter to setupRuby().