selftests/bpf: Fix subtest number formatting in test_progs

Remove weird spaces around / while preserving proper
indentation

Signed-off-by: Mykola Lysenko <mykolal@fb.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Daniel Müller <deso@posteo.net>
Link: https://lore.kernel.org/bpf/20220520070144.10312-1-mykolal@fb.com