src: make model counter in `GetCPUInfo()` unsigned

This fixes a compiler warning about comparing against
the (unsigned) `NODE_PUSH_VAL_TO_ARRAY_MAX` constant.

PR-URL: https://github.com/nodejs/node/pull/23880


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Sam Roberts <vieuxtech@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Eugene Ostroukhov <eostroukhov@google.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Matheus Marchini <mat@mmarchini.me>