Merge pull request #7149 from voxik/better-error-failure-for-exec-gem-uninstall

Report possible error prior checking output of gem uninstall

Author: deivid-rodriguez

test/rubygems/test_gem_commands_exec_command.rb

@@ -736,6 +736,8 @@ def test_gem_exec_gem_uninstall
       rescue StandardError
         nil
       end
+
+      assert_empty @ui.error
       refute_includes @ui.output, "running gem exec with"
       assert_includes @ui.output, "Successfully uninstalled a-2\n"