Commit 9dad94e7q ensured `test_data` is freed when a test is skipped,
but didn't ensure that when a whole test suite is skipped.

We are assuming the ownership of `test_data` is passed to GTestCase
with `g_test_add_data_func_full()` so free `test_data` always when
freeing a test case.

Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>