ZJIT was failing CI, adding this lock will probably fix it

This lock should have been there in the first place, and it was just
that the lock assertions weren't running in single ractor mode that we
failed to recognize the issue.

Author: luke-gruber

vm_method.c

@@ -1514,10 +1514,11 @@ rb_check_overloaded_cme(const rb_callable_method_entry_t *cme, const struct rb_c
         (int)vm_ci_argc(ci) == ISEQ_BODY(method_entry_iseqptr(cme))->param.lead_num) {
         VM_ASSERT(cme->def->type == VM_METHOD_TYPE_ISEQ, "type: %d", cme->def->type); // iseq_overload is marked only on ISEQ methods
 
-        cme = get_overloaded_cme(cme);
-
-        VM_ASSERT(cme != NULL);
-        METHOD_ENTRY_CACHED_SET((struct rb_callable_method_entry_struct *)cme);
+        RB_VM_LOCKING() {
+            cme = get_overloaded_cme(cme);
+            VM_ASSERT(cme != NULL);
+            METHOD_ENTRY_CACHED_SET((struct rb_callable_method_entry_struct *)cme);
+        }
     }
 
     return cme;