Issue 13243: Rename _Py_identifier to _Py_IDENTIFIER in asdl_c.py

Parser/asdl_c.py was missed in commit 7109f31300fb when _Py_identifier
was replaced with _Py_IDENTIFIER.  Thanks to Eric Snow for the patch.
diff --git a/Misc/ACKS b/Misc/ACKS
index 08531b9..e3e788e 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -899,6 +899,7 @@
 Gregory P. Smith
 Mark Smith
 Rafal Smotrzyk
+Eric Snow
 Dirk Soede
 Paul Sokolovsky
 Cody Somerville