tests: fix a memory leak in exit path
tests: fix a memory leak in exit path

When exiting normally we free all allocated resources (mostly to keep
valgrind quiet). The toolpath string is not being freed and pops up in
valgrind's "still reachable" category of leaks. Free this memory too
in the atexit() cleanup callback.

Signed-off-by: Bartosz Golaszewski <e5d45fddd9040473413b909b802f629a971ad04c@baylibre.com>

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