selftests/bpf: Skip timer_interrupt case when bpf_timer is not supported

Like commit fbdd61c9 ("selftests/bpf: Skip timer cases when bpf_timer is not supported"),
'timer_interrupt' test case should be skipped if verifier rejects
bpf_timer with returning -EOPNOTSUPP.

cd tools/testing/selftests/bpf
./test_progs -t timer
461     timer_interrupt:SKIP
Summary: 6/0 PASSED, 7 SKIPPED, 0 FAILED

Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://patch.msgid.link/20250915121657.28084-1-leon.hwang@linux.dev