Update kernel version to 6.5 in header constant tests

[Andreas Schwab]

On Sep 14 2023, Joseph Myers wrote:

> This patch updates the kernel version in the tests tst-mman-consts.py
> and tst-pidfd-consts.py to 6.5.  (There are no new constants covered
> by these tests in 6.5 that need any other header changes;
> tst-mount-consts.py was updated separately along with a header
> constant addition.)

Ok.

-- 
Andreas Schwab, SUSE Labs, schwab@suse.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
"And now for something completely different."