scx/selftests: Verify we can call create_dsq from prog_run

We already have some testcases verifying that we can call
BPF_PROG_TYPE_SYSCALL progs and invoke scx_bpf_exit(). Let's extend that to
also call scx_bpf_create_dsq() so we get coverage for that as well.

Signed-off-by: David Vernet <void@manifault.com>
Signed-off-by: Tejun Heo <tj@kernel.org>