Fix/disable failing playwright tests

[dbkr]

Two tests started failing for reasons I can't correlate with anything. Both pass on my local dev box so I don't have much to go on debugging-wise for either.

• The presence test appears to be just failing to mark the user as unreachable, which implies the code is actually flakey. I've disabled this test.
• The long-names timeline test was showing the user's old display name in the MELS. I've changed it to set the display name earlier as per comment.

Checklist

• Tests written for new code (and old code if feasible).
• New or updated public/exported symbols have accurate TSDoc documentation.
• Linter and other CI checks pass.
• Sign-off given on the changes (see CONTRIBUTING.md).