Fix minitest assertion for Ruby >= 3.4

Context:

Failure:
ActiveModel::Serializer::ReflectionTest#test_no_href_in_vanilla_reflection [/.rvm/gems/ruby-3.4.7/gems/minitest-5.10.3/lib/minitest/assertions.rb:139]:
Expected /undefined method `href'/ to match # encoding: US-ASCII
"undefined method 'href' for an instance of ActiveModel::Serializer::HasOneReflection".

Author: wasifhossain

test/serializers/reflection_test.rb

@@ -383,7 +383,10 @@ def test_no_href_in_vanilla_reflection
         exception = assert_raise(NoMethodError) do
           reflection.instance_eval(&link)
         end
-        assert_match(/undefined method `href'/, exception.message)
+
+        expected = RUBY_VERSION >= '3.4.0' ? /undefined method 'href'/ : /undefined method `href'/
+
+        assert_match(expected, exception.message)
       end
 
       # rubocop:disable Metrics/AbcSize