Add addGCReference call also to builtin hasattr

this got introduced in c9598857 for getattr

src/runtime/builtin_modules/builtins.cpp

@@ -641,8 +641,15 @@ Box* hasattrFuncInternal(BoxedFunctionBase* func, CallRewriteArgs* rewrite_args,
         // value is fixed.
         if (!PyString_CheckExact(_str) && !PyUnicode_CheckExact(_str))
             rewrite_args = NULL;
-        else
+        else {
+            if (PyString_CheckExact(_str) && PyString_CHECK_INTERNED(_str) == SSTATE_INTERNED_IMMORTAL) {
+                // can avoid keeping the extra gc reference
+            } else {
+                rewrite_args->rewriter->addGCReference(_str);
+            }
+
             rewrite_args->arg2->addGuard((intptr_t)arg2);
+        }
     }
 
     _str = coerceUnicodeToStr<S>(_str);