Update installer.sh.j2

[Gankra]

Lots of improvements to downstream from https://sh.rustup.rs

Notably this (astral-sh/uv#12780):

if ! (ensure grep '^Features' /proc/cpuinfo | grep -E -q 'neon|simd') ; then
    # Either `/proc/cpuinfo` is malformed or unavailable, or
    # at least one processor does not have NEON (which is asimd on armv8+).
    _cputype=arm
fi