turnip/ci: bump the a750_vk timeout

We already managed to hit the timeout once, and since the job is manual
anyway, let's bump it generously so as to also allow for more tests
to be added without having to bump the timeout every time.

Signed-off-by: Martin Roukala (né Peres) <martin.roukala@mupuf.org>
Part-of: <!29381>