build: don't run test-asan workflow on non-master pushes

PR-URL: https://github.com/nodejs/node/pull/34509
Refs: https://github.com/nodejs/node/pull/34464


Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Matheus Marchini <mat@mmarchini.me>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>