ktest.pl: Always warn on build warnings

If a warning happens at build, give a warning at the end:

  Build time:   1 minute 40 seconds
  Install time: 17 seconds
  Reboot time:  25 seconds

  *** WARNING found in build: 1 ***

  *******************************************
  *******************************************
  KTEST RESULT: TEST 1 SUCCESS!!!!   **
  *******************************************
  *******************************************

This way, even if the test isn't made to fail on warnings during the
build, a message is still displayed that warnings were found.

Link: https://lore.kernel.org/<20240819172028.3a7fae09@gandalf.local.home

>
Acked-by: John 'Warthog9' Hawley (Tenstorrent) <warthog9@eaglescrag.net>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>