Update kernel version to 6.9 in header constant tests

[Andreas Schwab]

On Mai 23 2024, Joseph Myers wrote:

> This patch updates the kernel version in the tests tst-mman-consts.py
> and tst-mount-consts.py to 6.9.  (There are no new constants covered
> by these tests in 6.9 that need any other header changes;
> tst-pidfd-consts.py was updated separately along with adding new
> constants relevant to that test.)

Ok.

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Andreas Schwab, SUSE Labs, schwab@suse.de
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