Run isolated specs on the oldest CRuby too

Author: eregon

.github/workflows/ci.yml

@@ -33,13 +33,17 @@ jobs:
   isolated:
     name: "Test isolated"
     runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        ruby: [ 2.3, 3.2 ] # oldest and latest CRuby
     env:
       RUBYOPT: '-w'
     steps:
       - uses: actions/checkout@v3
       - uses: ruby/setup-ruby@v1
         with:
-          ruby-version: 3.2
+          ruby-version: ${{ matrix.ruby }}
           bundler-cache: true
       - run: bundle exec rake compile
       - run: bundle exec rake spec:isolated

lib/concurrent-ruby/concurrent/atomic/locals.rb

@@ -1,8 +1,7 @@
+require 'fiber'
 require 'concurrent/utility/engine'
 require 'concurrent/constants'
 
-require 'fiber'
-
 module Concurrent
   # @!visibility private
   # @!macro internal_implementation_note