Log Message:
py-pandas: fix (sandboxed) non-default Python builds

Another issue where Meson isn't versioned in pkgsrc, so we end up with
it "helpfully" supplying the path to Python it believes is correct,
which is wrong for any non-default Python version. (The 2.1.0 version
of this package carried a similar fix, which was removed in the update
to 2.1.1; a variation of it is restored here.)

Separately, this package directly expresses a minimum Meson version, so
reflect that as well.