selftests: gpio: gpio-aggregator: add a test case for _sysfs prefix reservation
The kernel doc for gpio-aggregator configfs interface, which was recently
added, states that users should not be able to create an aggregator with a
name prefixed by "_sysfs" via configfs. However, it was found that this
guard does not function as expected (thanks to Dan Carpenter for
identifying and fixing the issue).
Add a test case to verify the guard.
Signed-off-by: Koichiro Den <koichiro.den@canonical.com>
Link: https://lore.kernel.org/r/20250412150119.1461023-1-koichiro.den@canonical.com
Signed-off-by: Bartosz Golaszewski <brgl@bgdev.pl>