"bundle" from bundler conflicts with truffleruby-head/bin/bundle

[eregon]

From https://github.com/ruby-syntax-tree/syntax_tree/actions/runs/3429160877/jobs/5714402479
cc @kddnewton

Can be reproduced locally:

~ ∴ chruby dev
Using truffleruby-dev: truffleruby 23.0.0-dev-baac89dc, like ruby 3.1.2, GraalVM CE Native [x86_64-linux]
~ ∴ bundle --version                                    
Bundler version 2.3.7
~ ∴ gem i bundler -v 2.3.6
Fetching bundler-2.3.6.gem
bundler's executable "bundle" conflicts with /home/eregon/.rubies/truffleruby-dev/bin/bundle
Overwrite the executable? [yN]  
ERROR:  Error installing bundler:
	"bundle" from bundler conflicts with /home/eregon/.rubies/truffleruby-dev/bin/bundle
zsh: exit 1     gem i bundler -v 2.3.6

Here is the original bundle file.
Seems newer RubyGems doesn't like it even with the This file was generated by RubyGems. on line 3?

$ cat /home/eregon/.rubies/truffleruby-dev/bin/bundle
#!/usr/bin/env bash
#
# This file was generated by RubyGems.
# The above lines match the format expected by rubygems/installer.rb check_executable_overwrite
# bash section ignored by the Ruby interpreter

# get the absolute path of the executable and resolve symlinks
SELF_PATH=$(cd "$(dirname "$0")" && pwd -P)/$(basename "$0")
while [ -h "$SELF_PATH" ]; do
  # 1) cd to directory of the symlink
  # 2) cd to the directory of where the symlink points
  # 3) get the pwd
  # 4) append the basename
  DIR=$(dirname "$SELF_PATH")
  SYM=$(readlink "$SELF_PATH")
  SELF_PATH=$(cd "$DIR" && cd "$(dirname "$SYM")" && pwd)/$(basename "$SYM")
done
exec "$(dirname $SELF_PATH)/ruby" "$SELF_PATH" "$@"

#!ruby
#
# This file was generated by RubyGems.
#
# The application 'bundler' is installed as part of a gem, and
# this file is here to facilitate running it.
#

require 'rubygems'

version = ">= 0.a"

str = ARGV.first
if str
  str = str.b[/\A_(.*)_\z/, 1]
  if str and Gem::Version.correct?(str)
    version = str
    ENV['BUNDLER_VERSION'] = str

    ARGV.shift
  end
end

if Gem.respond_to?(:activate_bin_path)
load Gem.activate_bin_path('bundler', 'bundle', version)
else
gem "bundler", version
load Gem.bin_path("bundler", "bundle", version)
end

[eregon]

https://github.com/rubygems/rubygems/pull/2929/files#diff-b25097522a961ed7158012499383b8a8057caf87cbc445d6b168a5b8a27ba45dR224 is what caused the new failure, together with our bin/ scripts design: https://github.com/oracle/truffleruby/blob/master/doc/contributor/launchers.md

I worked around it in setup-ruby to fix it as fast as possible: ruby/setup-ruby@f2c070b
And that fixes the build: https://github.com/ruby-syntax-tree/syntax_tree/actions/runs/3429563818/jobs/5715726788

I'll also fix it in TruffleRuby (will take a bit longer to merge and build a dev build), and then the harder part making a test for this which seems quite tricky.
Alternatively, longer-term we should probably use the pure-Ruby bin/ scripts, even though that can cause issues if truffleruby is not in PATH.