tests: tweak a log message
tests: tweak a log message

Drop the 'test' prefix from the message displayed when running
a test. We're already stating that in the message header.

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

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