selftests/mm: add pkey_sighandler_xx, hugetlb_dio to .gitignore

selftests/mm: add pkey_sighandler_xx, hugetlb_dio to .gitignore

Commit 6998a73efbb8 ("selftests/mm: Add new testcases for pkeys") and
commit 3a103b5315b7 ("selftest: mm: Test if hugepage does not get leaked
during __bio_release_pages()") generate test binaries hugetlb_dio,
pkey_sighandler_tests_32 and pkey_sighandler_tests_64 but did not add
these to .gitignore.  Correct this.

Link: https://lkml.kernel.org/r/20240924185911.117937-1-lorenzo.stoakes@oracle.com
Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Donet Tom <donettom@linux.ibm.com>
Cc: Keith Lucas <keith.lucas@oracle.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>