selftests: bpf: add missing executables to .gitignore

commit 435f90a3 ("selftests/bpf: add a test case for sock_ops
perf-event notification") missed adding new test to gitignore.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

tools/testing/selftests/bpf/.gitignore

@@ -27,3 +27,4 @@ test_flow_dissector
 flow_dissector_load
 test_netcnt
 test_section_names
+test_tcpnotify_user