support/testing: fix job check-gitlab-ci.yml

Currently 'run-tests -l' is broken. It breaks 'make .gitlab-ci.yml' that
in turn breaks the job in GitLab.

TestRustBase is not a test case by itself, so it can't have a method
with the name starting with "test_" otherwise nose2 assumes it is a test
case.
Move the test_run method from the base class to the derived classes.

While at it, update .gitlab-ci.yml with the new test cases.

Fixes:
https://gitlab.com/buildroot.org/buildroot/-/jobs/52000035



Reported-by: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: Ricardo Martincoski <ricardo.martincoski@gmail.com>
Cc: Eric Le Bihan <eric.le.bihan.dev@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Yann E. MORIN <yann.morin.1998@free.fr>
Cc: Yegor Yefremov <yegorslists@googlemail.com>
Reviewed-by: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>