Before this change, filtered test runs still built every gtest target
because `test_results` depended on all unit and functional gtest targets.
This updates both `px4_add_unit_gtest()` and `px4_add_functional_gtest()`
to use the filtered dependency helper so filtered runs only build the
selected targets.
Signed-off-by: Onur Özkan <work@onurozkan.dev>