support/testing/tests/package/test_docker-compose: fix docker compose binary name

Docker compose is now invoked as "docker compose" not "docker-compose."

Fixes:

  https://gitlab.com/buildroot.org/buildroot/-/jobs/3249828442



Signed-off-by: Christian Stewart <christian@paral.in>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>