selftests: Add missing gitignore entries

Prevent them from polluting git status after building selftests.

Signed-off-by: Gabriel Krisman Bertazi <[e-mail]>
Signed-off-by: Shuah Khan <[e-mail]>

tools/testing/selftests/firmware/.gitignore

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

tools/testing/selftests/netfilter/.gitignore

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

tools/testing/selftests/ptrace/.gitignore

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