selftests: acct: Add ksft_exit_skip if not running as root

selftests: acct: Add ksft_exit_skip if not running as root

If the selftest is not running as root, it should skip not
fail and give an appropriate warning to the user. This patch adds
ksft_exit_skip() if the test is not running as root.

Logs:

Before change:

TAP version 13
1..1
ok 1 # SKIP This test needs root to run!

After change:

TAP version 13
1..1
ok 2 # SKIP This test needs root to run!
Totals: pass:0 fail:0 xfail:0 xpass:0 skip:1 error:0

Link: https://lore.kernel.org/r/20241210123212.332050-1-cvam0000@gmail.com
Signed-off-by: Shivam Chaudhary <cvam0000@gmail.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>