tests: Add basic test coverage for our seccomp filters

In particular, this checks that CVE-2017-5226, CVE-2019-10063 and
CVE-2021-41133 are still prevented.

Signed-off-by: Simon McVittie <smcv@collabora.com>
(cherry picked from commit 7c5aec474c)
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Internal Server Error - Gitea: Git with a cup of tea
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Gitea Version: 1.28.0+dev-477-g8b6ad49a5f