selftests/mm: run_vmtests.sh: add hugetlb test category

The usage of run_vmtests.sh does not include hugetlb, which is a valid
test category.

Add the 'hugetlb' to the usage of run_vmtests.sh.

Link: https://lkml.kernel.org/r/20240129115246.1234253-1-leitao@debian.org


Signed-off-by: Breno Leitao <leitao@debian.org>
Reviewed-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Reviewed-by: Joel Savitz <jsavitz@redhat.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>