[3.10] bpo-37602: Clarify that the lib2to3 nonzero fixer changes only definitions (GH-30075) (GH-30085)

(cherry picked from commit 481f3ffdbe40bd19677a1ba0ac2e7cece8949b47)

Co-authored-by: Irit Katriel <1055913+iritkatriel@users.noreply.github.com>
1 file changed