selftests: Add missing gitignore entries

Prevent them from polluting git status after building selftests.
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/selftests/firmware/.gitignore

+# SPDX-License-Identifier: GPL-2.0-only
+fw_namespace

tools/testing/selftests/netfilter/.gitignore

+# SPDX-License-Identifier: GPL-2.0-only
+nf-queue

tools/testing/selftests/ptrace/.gitignore

 # SPDX-License-Identifier: GPL-2.0-only
 get_syscall_info
 peeksiginfo
+vmaccess