fix Issue 8366 - Overriding const member function in conjunction with…

… mutable overload causes a strange error

src/object_.d

@@ -689,7 +689,7 @@ class TypeInfo_AssociativeArray : TypeInfo
                     this.value == c.value;
     }
 
-    override hash_t getHash(in void* p) nothrow @trusted
+    override hash_t getHash(in void* p) nothrow @trusted const
     {
         return _aaGetHash(cast(void*)p, this);
     }