"tails-security-check is using the Tails-specific SocksPort" test is broken when there's a live security advisory

We currently have a live security advisory for #16694 (closed), which breaks this test, probably due to the fact tails-security-check is already running. IMO the “I re-run tails-security-check” step should do systemctl --user restart tails-security-check.service, so that:

1. any already running tails-security-check is killed, which should fix this bug
2. we test tails-security-check in an environment closer to how it’s run in a real Tails: as we can see on #16603, running this kind of scripts via systemd or without it can yield subtly different behavior

Feature Branch: https://salsa.debian.org/tails-team/tails/merge_requests/20

Related issues

• Blocks #16209

Original created by @intrigeri on 16701 (Redmine)