Update kernel version to 6.13 in header constant tests

[Florian Weimer]

* Joseph Myers:

> There are no new constants covered by tst-mman-consts.py,
> tst-mount-consts.py or tst-sched-consts.py in Linux 6.13 that need any
> header changes, so update the kernel version in those tests.
> (tst-pidfd-consts.py will need updating separately along with adding
> new constants to glibc.)
>
> Tested with build-many-glibcs.py.

Looks okay.

Reviewed-by: Florian Weimer <fweimer@redhat.com>

Thanks,
Florian