bpo-40903: Handle multiple '=' in invalid assignment rules in the PEG parser (GH-20697)



Automerge-Triggered-By: @pablogsal
diff --git a/Parser/pegen/pegen.c b/Parser/pegen/pegen.c
index afe75d7..7b581ca 100644
--- a/Parser/pegen/pegen.c
+++ b/Parser/pegen/pegen.c
@@ -161,6 +161,7 @@
 const char *
 _PyPegen_get_expr_name(expr_ty e)
 {
+    assert(e != NULL);
     switch (e->kind) {
         case Attribute_kind:
             return "attribute";