gh-114058: More robust method handling in redundancy eliminator (GH-115779)

Python/optimizer_analysis.c

@@ -315,6 +315,7 @@ sym_new_known_notnull(_Py_UOpsAbstractInterpContext *ctx)
     if (res == NULL) {
         return NULL;
     }
+    sym_set_flag(res, KNOWN);
     sym_set_flag(res, NOT_NULL);
     return res;
 }