Don't reach into .mt directly (#31063)

Author: Keno

base/reflection.jl

@@ -967,10 +967,10 @@ function may_invoke_generator(method::Method, @nospecialize(atypes), sparams::Si
     # For now, only handle the (common, generated by the frontend case) that the
     # generator only has one method
     isa(method.generator, Core.GeneratedFunctionStub) || return false
-    generator_mt = typeof(method.generator.gen).name.mt
-    length(generator_mt) == 1 || return false
+    gen_mthds = methods(method.generator.gen)
+    length(gen_mthds) == 1 || return false
 
-    generator_method = first(MethodList(generator_mt))
+    generator_method = first(gen_mthds)
     nsparams = length(sparams)
     isdefined(generator_method, :source) || return false
     code = generator_method.source