man/man2/open.2: Fix doc for O_CREAT | O_DIRECTORY

man/man2/open.2: Fix doc for O_CREAT | O_DIRECTORY

Although Linux kernels before 5.7 would create a regular file when
opening a nonexistent file with O_CREAT | O_DIRECTORY, this behavior
was changed to something deeply buggy in 5.7, and when the bug was
fixed in 6.4 this combination of open flags became invalid.

Adjust the documentation to match the 6.4+ behavior,
which makes more sense anyway.

Signed-off-by: Paul Eggert <eggert@cs.ucla.edu>
Message-ID: <20250530072029.344532-1-eggert@cs.ucla.edu>
Signed-off-by: Alejandro Colomar <alx@kernel.org>