libjxl: FTBFS because of timeout in test

[Mathieu Malaterre <malat@debian.org>]

[cc me please]

Dear hurd porters,

libjxl is currently in FTBFS state:

* https://buildd.debian.org/status/fetch.php?pkg=jpeg-xl&arch=hurd-i386&ver=0.7.0-5&stamp=1664979667&raw=0

libjxl is supposed to build & run on all x86 system out there
(portable c++ code). Please advise on best solution to work around the
timeout issue in the (long) running test.

Thanks& Regards