[automated testing] debian testing: compile failure with qt6

[José Matos]

On Sat, 2025-05-10 at 01:34 +0000, testing at tester.lyx.org wrote:
> insets/InsetFloat.cpp:376:1: error: control reaches end of non-void function

FWIW that is the only warning.

I am not sure if using -Werror=return-type fails after the first warning or not.
:-)

Regards,
-- 
José Abílio