pmb checksum fails with abuild permission denied creating /dev/null"

Using pmb from git master (as of today):

$ pmbootstrap checksum abuild
...

[10:43:08] (native) generate checksums for abuild
[10:43:08] (native) % cd /home/pmos/build; busybox su pmos -c HOME=/home/pmos abuild checksum ;
[10:43:08] run: ['doas', 'env', '-i', '/bin/sh', '-c', 'CHARSET=UTF-8 HISTFILE=\'~/.ash_history\' HOME=/root LANG=UTF-8 PATH=/usr/lib/ccache/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin PYTHONUNBUFFERED=1 SHELL=/bin/ash TERM=xterm /usr/sbin/chroot /home/clayton/.local/var/pmbootstrap_systemd/chroot_native /bin/sh -c \'cd /home/pmos/build;busybox su pmos -c \'"\'"\'HOME=/home/pmos abuild checksum ;\'"\'"\' ;\' ;']
/usr/sbin/abuild: /usr/share/abuild/functions.sh: line 110: can't create /dev/null: Permission denied
/usr/sbin/abuild: /usr/share/abuild/functions.sh: line 166: can't create /dev/null: Permission denied
Unable to deduce build architecture. Install apk-tools, or set CBUILD.

To reproduce:

• checkout pmaports branch: https://gitlab.com/postmarketOS/pmaports/-/merge_requests/5319

• pmbootstrap checksum abuild

Note that in that branch, I'm upgrading/changing the abuild package in the local repo... I don't think it would cause this failure but I've also never seen this failure before so... 🤷