[3.7] bpo-32711: Fix warnings for Python/ast_unparse.c (GH-5426) (#5475)

* bpo-32711: Fix warnings for Python/ast_unparse.c
(cherry picked from commit 83ab995871ffd504ac229bdbf5b9e9ffc1032815)

Co-authored-by: Stéphane Wirtel <stephane@wirtel.be>
2 files changed