build: Raise required wayland-scanner version to 1.23.0 for tests

It's needed for the deprecated-since attribute [1] introduced with [2],
at least when building the tests, which pass the '--strict' parameter to
wayland-scanner.

[1] wayland/wayland@ee12e69b


[2] 6c214e6d

Signed-off-by: Heiko Becker <mail@heiko-becker.de>