x11-toolkits/wlroots: backport fix for TTY > 10

$ sway -d
[...]
[sway/server.c:39] Preparing Wayland server initialization
[backend/session/direct-freebsd.c:159] Using tty /dev/ttyv10
[backend/session/direct-freebsd.c:163] Cannot open tty: No such file or directory
[backend/session/session.c:96] Failed to load session backend
[backend/backend.c:321] Failed to start a DRM session
[backend/noop/backend.c:51] Creating noop backend
[sway/server.c:46] Unable to create backend

PR: 242801
Submitted by: Ting-Wei Lan