EDIT: works after downgrading OpenSSH, turns out even EOL Alpine version got updated packages!
Also didn't have much luck on Alpine 3.20.10 with OpenSSH_9.7p1 which I've freshly installed from an official ISO.
Last two entries in /etc/shadow:
test:*:20762:0:99999:7:::
q3k:$6$snip.GgDQNTrqqX.A0:20762:0:99999:7:::
SSHing into test@ with one 'wrong' password then one 'long' password doesn't work. I have UsePAM no and PasswordAuthentication yes in my sshd_config.