selftests/mqueue: Fix incorrectly named file

Commit 85506aca2eb4 ("selftests/mqueue: Set timeout to 180 seconds")
intended to increase the timeout for mq_perf_tests from the default
kselftest limit of 45 seconds to 180 seconds.

Unfortunately, the file storing this information was incorrectly named
`setting` instead of `settings`, causing the kselftest runner not to
pick up the limit and keep using the default 45 seconds limit.

Fix this by renaming it to `settings` to ensure that the kselftest
runner uses the increased timeout of 180 seconds for this test.

Fixes: 85506aca2eb4 ("selftests/mqueue: Set timeout to 180 seconds")
Cc: <stable@vger.kernel.org> # 5.10.y
Signed-off-by: Simon Liebold <simonlie@amazon.de>
Link: https://lore.kernel.org/r/20260312140200.2224850-1-simonlie@amazon.de
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>