support/testing: test_docker_compose: bump the kernel to 4.19.204

gcc 10.x is now used by default but the kernel 4.19 used by
test_docker_compose doesn't build with it.

Bump the kernel to 4.19.204 release that contains a lot of
fixes for newer gcc.

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>