lib/Kconfig.debug: move int_pow test option to runtime testing section

lib/Kconfig.debug: move int_pow test option to runtime testing section

When executing 'make menuconfig' with KUNIT enabled, the int_pow test
option appears on the first page of the main menu instead of under the
runtime testing section.  Relocate the int_pow test configuration to the
appropriate runtime testing submenu, ensuring a more organized and logical
structure in the menu configuration.

Link: https://lkml.kernel.org/r/20241005222221.2154393-1-visitorckw@gmail.com
Fixes: 7fcc9b53216c ("lib/math: Add int_pow test suite")
Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
Cc: Ching-Chun (Jim) Huang <jserv@ccns.ncku.edu.tw>
Cc: David Gow <davidgow@google.com>
Cc: Luis Felipe Hernandez <luis.hernandez093@gmail.com>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>