test: fix python-version selection with actions

s/PYTHON\_VERSION/python-version

Refs: https://github.com/actions/setup-python

PR-URL: https://github.com/nodejs/node/pull/32609


Reviewed-By: Matheus Marchini <mat@mmarchini.me>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Yongsheng Zhang <zyszys98@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>