kunit: tool: add test to check parsing late test plan

Add test to check for the infinite loop caused by the inability
to parse a late test plan.

The test parses the following output:
 TAP version 13
 ok 4 test4
 1..4

Link: https://lore.kernel.org/r/20250313192714.1380005-1-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>