kunit: tool: fix count of tests if late test plan

Fix test count with late test plan.

For example,
  TAP version 13
  ok 1 test1
  1..4

Returns a count of 1 passed, 1 crashed (because it expects tests after
the test plan): returning the total count of 2 tests

Change this to be 1 passed, 1 error: total count of 1 test

Link: https://lore.kernel.org/r/20250319223351.1517262-1-rmoar@google.com


Signed-off-by: Rae Moar <rmoar@google.com>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Shuah Khan <shuah@kernel.org>