selftests: seccomp: update .gitignore with newly added tests

Update .gitignore with newly added tests.

Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>
Acked-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>

tools/testing/selftests/seccomp/.gitignore

@@ -1 +1,2 @@
 seccomp_bpf
+seccomp_benchmark