lib: Ensure prime numbers tests are included in KUnit test runs

When the select of PRIME_MUMBERS was removed from it's KUnit test
Kconfig nothing was added to the KUnit configs, meaning that when run
via the KUnit runner the tests are neither built nor run.  Add
PRIME_NUMBERS to all_tests.config so they are enabled when the KUnit
runner builds the kernel.

Fixes: 3f292517 ("lib/prime_numbers: KUnit test should not select PRIME_NUMBERS")
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20250422-lib-fix-prime-numbers-kunit-v1-1-4278c1d4a4ae@kernel.org


Signed-off-by: Kees Cook <kees@kernel.org>