make PyGrammar_LabelRepr return a const char * (closes #16369)
diff --git a/Parser/grammar1.c b/Parser/grammar1.c
index 1f7d264..4b5aa8a 100644
--- a/Parser/grammar1.c
+++ b/Parser/grammar1.c
@@ -30,7 +30,7 @@
 #endif
 }
 
-char *
+const char *
 PyGrammar_LabelRepr(label *lb)
 {
     static char buf[100];