Add ruby-4.0.0

Skip saving cache for merge_group event

Fix rubyinstaller2 urls for latest release

Update CRuby releases on Windows

Add ruby-4.0.0-preview3

Add ruby-3.4.8

When setting $JAVA_HOME also add $JAVA_HOME/bin to PATH

* See discussion in rake-compiler/rake-compiler#247
  it is messy if that's not the case and also creates inconsistencies
  based on which Java tool/executable is used.

Account for Bundler 4

* Fixes #827

Test Ruby 4.0 previews

exec.exec() only accepts strings