selftests/bpf: Fix .gitignore to not ignore test_progs.c

List all possible test_progs flavors explicitly to avoid accidentally
ignoring valid source code files. In this case, test_progs.c was still
ignored after recent 809ed84d ("selftests/bpf: Whitelist test_progs.h
from .gitignore") fix that added exception only for test_progs.h.

Fixes: 74b5a596 ("selftests/bpf: Replace test_progs and test_maps w/ general rule")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20210914162228.3995740-1-andrii@kernel.org

tools/testing/selftests/bpf/.gitignore

@@ -9,8 +9,9 @@ test_tag
 FEATURE-DUMP.libbpf
 fixdep
 test_dev_cgroup
-/test_progs*
-!test_progs.h
+/test_progs
+/test_progs-no_alu32
+/test_progs-bpf_gcc
 test_verifier_log
 feature
 test_sock