Bug#1116709: hw-detect: list_deb_firmware() does not find files in trixie packages after /usr merge

[Andrew Kornilov <akornilov@gmail.com>]

Update on this bug:

1. With debian-installer 20250803+deb13u1 and hw-detect 1.171, the firmware for the laptop’s network card won’t install. The installer freezes at “Detect network hardware.”
In /var/log/syslog the last line is: hw-detect exited nonzero.

2. After applying this patch, everything works: the install finishes and the firmware gets installed.