Gem commands use system Ruby instead of project Ruby, causing ruby-lsp installation to fail

[gfguthrie]

I'm using chruby via direnv, and get the following error on macOS when the extension attempts to install ruby-lsp:

from extension "Ruby" version 0.16.10: Failed to install gem 'ruby-lsp': Gem command failed (status: 1)
Error: ERROR:  Error installing ruby-lsp:
    There are no versions of prism (>= 1.6.0) compatible with your Ruby & RubyGems.
    prism requires Ruby version >= 2.7.0. The current ruby version is 2.6.10.210.

As I was messing about with my environment I would sometimes get a different error:

dlopen(.../.gem/ruby/3.4.8/gems/date-3.4.1/lib/date_core.bundle): Symbol not found: _rb_cFalseClass
Expected in: /System/Library/Frameworks/Ruby.framework/Versions/2.6/usr/bin/ruby

I eventually just installed it myself to bypass the the extension attempting to install the gem and everything is now working correctly.

However, after looking at the code I believe these errors can be resolved by using worktree.which() in gemset.rs to find the correct ruby & gem executables first instead of just doing a bare execute.