Update kernel version to 6.10 in header constant tests

This patch updates the kernel version in the tests tst-mman-consts.py,
tst-mount-consts.py, and tst-pidfd-consts.py to 6.9.

There are no new constants covered by these tests in 6.10.

Tested with build-many-glibcs.py.
Reviewed-by: Florian Weimer <fweimer@redhat.com>