build: update minimum AIX OS level

Update minimum AIX OS level to 7.2 TL2. Looks like this
will be the version we can get into the CI so should be the
base level for 13.X and above and will be in support for the life
of 13.X.

PR-URL: https://github.com/nodejs/node/pull/29476


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: Minwoo Jung <minwoo@nodesource.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>