tests: make gpiod-unit.h a source for gpiod-unit
tests: make gpiod-unit.h a source for gpiod-unit

Listing gpiod-unit.h as a source for the gpiod-unit binary ensures that
it is properly tracked as a dependency and that it will be included in
distribution tarballs.

Signed-off-by: Thierry Reding <3055038c414aef68bf32c33b8118623e7554e0f2@nvidia.com>
Signed-off-by: Bartosz Golaszewski <108de5fbc428215dc26df4468b48691526611148@gmail.com>

brgl/libgpiod,brgl/libgpiod,brgl/libgpiod,brgl/libgpiod