selftests/bpf: disable program test run for progs/refcounted_kptr.c

selftests/bpf: disable program test run for progs/refcounted_kptr.c

Florian Westphal found a bug in test_loader.c processing of __retval
tag. Because of this bug the function test_loader.c:do_prog_test_run()
never executed and all __retval test tags were ignored. This hid an
issue with progs/refcounted_kptr.c tests.

When __retval tag bug is fixed and refcounted_kptr.c tests are run
kernel reports various issues and eventually hangs. Shortest reproducer
is the following command run a few times:

  $ for i in $(seq 1 4); do (./test_progs --allow=refcounted_kptr &); done

Commenting out __retval tags for these tests until this issue is resolved.

Reported-by: Florian Westphal <fw@strlen.de>
Link: https://lore.kernel.org/bpf/f4c4aee644425842ee6aa8edf1da68f0a8260e7c.camel@gmail.com/T/
Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20230420232317.2181776-2-eddyz87@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>