Prevent app updates to stop NC server

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Is your feature request related to a problem? Please describe.
I've experienced multiple times that app updates put the NC server to maintenance mode (e.g. https://github.com/nextcloud/mail/issues/11743). This is extremely painful, especially with managed instances like Hetzner Storage Share.

Describe the solution you'd like
Mitigation: The NC server remains operational even though an update/migration routine failed.

Describe alternatives you've considered
Prevention: DevOps prevents faulty app updates to be shipped by testing deployment in CI. This must include migration from previous versions.

Additional context
Issue copied from https://github.com/nextcloud/mail/issues/11757

Start by reviewing the reported failure scenario and the linked nextcloud/mail issues, then trace how app updates and migrations affect the Nextcloud server. The issue does not name files, tests, or an entry point; work is done only when a concrete, tested approach prevents or mitigates a failed update from leaving the server in maintenance mode.