The recent optimization of not running "mkinitfs" during the trigger
script when running in pmbootstrap lead to unexpected behavior for some
use cases: testing initramfs changes and upgrading the initramfs in the
chroot (e.g. with pmbootstrap chroot --image). Let the user know that it
gets skipped and tell them how they can force building a new initramfs,
as discussed with Caleb.

[ci:skip-build]: already built successfully in CI