tests: remove the MALLOC attribute from xappend()
tests: remove the MALLOC attribute from xappend()

The internally called realloc() doesn't have this attribute so we
can't propagate it up the stack.

Signed-off-by: Bartosz Golaszewski <108de5fbc428215dc26df4468b48691526611148@gmail.com>

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