Load the worktree RubyGems in the dev bundle binstub

After flattening, lib/ holds both RubyGems and Bundler, so activating the
Bundler gemspec prepends the worktree lib/ over the already-booted system
RubyGems. That partial overlay mixes a worktree Gem with an older system
Gem::ConfigFile, which breaks native extension installs on Ruby 3.2/3.3
(undefined install_extension_in_lib) and corrupts spec names elsewhere.

Route bin/bundle through switch_rubygems like bin/rspec and bin/test-unit
so it re-execs onto the worktree RubyGems consistently. Point the shared
gem home job at the worktree copy too, since the dev binstub can no longer
load a separately installed RubyGems, and the matrix is redundant for now.

Author: hsbt

.github/workflows/install-rubygems.yml

@@ -174,16 +174,8 @@ jobs:
         with:
           ruby-version: 3.2
           bundler: none
-      - name: Save system RubyGems version to ENV
-        run: |
-          RGV=$(ruby -e 'puts Gem::VERSION.split(".")[0..2].join(".")')
-          echo "RGV=v$RGV" >> $GITHUB_ENV
-        if: matrix.rubygems == 'system'
-      - name: Set dev RubyGems version
-        run: |
-          RGV=..
-          echo "RGV=v$RGV" >> $GITHUB_ENV
-        if: matrix.rubygems == 'dev'
+      - name: Use the worktree RubyGems
+        run: echo "RGV=." >> $GITHUB_ENV
       - name: Setup app depending on psych with initial Ruby
         run: mkdir foo && cd foo && ../bin/bundle init && ../bin/bundle add psych -v 5.1.2
         shell: bash

bin/bundle

@@ -1,6 +1,7 @@
 #!/usr/bin/env ruby
 # frozen_string_literal: true
 
+require_relative "../spec/support/switch_rubygems"
 require_relative "../spec/support/activate"
 
 load File.expand_path("bundle", Spec::Path.exedir)