Merge branch 'brodock-fix-preflight' into 'main'

Ensure Bunder.with_unbundled_env is used for preflight-checks

Closes #2039

See merge request https://gitlab.com/gitlab-org/gitlab-development-kit/-/merge_requests/3558



Merged-by: Nao Hashizume <nhashizume@gitlab.com>
Approved-by: Nao Hashizume <nhashizume@gitlab.com>
Reviewed-by: Nao Hashizume <nhashizume@gitlab.com>
Co-authored-by: Gabriel Mazetto <gabriel@gitlab.com>

lib/gdk/diagnostic/ruby_gems.rb

@@ -50,7 +50,15 @@ def gem_installed?(name)
       end
 
       def gem_loads_ok?(name)
-        exec_cmd("#{bundle_exec_cmd} ruby -r #{name} -e 'nil'")
+        command = -> { exec_cmd("#{bundle_exec_cmd} ruby -r #{name} -e 'nil'") }
+
+        if bundler_available?
+          ::Bundler.with_unbundled_env do
+            command.call
+          end
+        else
+          command.call
+        end
       end
 
       def exec_cmd(cmd)
@@ -59,6 +67,10 @@ def exec_cmd(cmd)
         Shellout.new(cmd, chdir: config.gitlab.dir.to_s).execute(display_output: false, display_error: false).success?
       end
 
+      def bundler_available?
+        defined? ::Bundler
+      end
+
       def gitlab_error_message
         <<~MESSAGE
           The following Ruby Gems appear to have issues: