twister: fix skip marked as pass in json report

When some testcase is skip in their source code by ztest_test_skip()
function in final json report it is marked as pass what is wrong. Due to
the changes in this commit those skips can be marked properly.

Fixes: #41440

Signed-off-by: Piotr Golyzniak <piotr.golyzniak@nordicsemi.no>