Update zeratax/matrix-registration Docker tag to v0.9.1

[renovate]

This PR contains the following updates:

Package	Update	Change
zeratax/matrix-registration	minor	v0.7.2 -> v0.9.1

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[aine-etke]

WARNING: API changed a lot, playbook needs to be updated to handle that change

[spantaleev]

Definitely. We have the following bugs open:

• Database initialization during startup fails zeratax/matrix-registration#73
• Running alembic via the container image is problematic zeratax/matrix-registration#72

Until they're fixed (and we likely do other migration changes), we can't merge it. It seems like the project is unmaintained anyway, so being stuck on the old version is as good as being stuck on the slightly-newer one.