fix: avoid outer "uncaught exception" for ServerMaintenanceMode

[joshtrichards]

• Resolves: [Bug]: Nextcloud reports errors with carddav/caldav requests in maintenance mode #55894

Summary

We already exclude ServerMaintenanceMode in the inner logger, but there are some spots where it can can bubble up still via DAV.

TODO

• ...

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

[joshtrichards]

/backport to stable32

[joshtrichards]

/backport to stable31

[kesselb]

I can't fully explain why, but I'd prefer to fix this in remote.php's handleException. I think we already handle it in the else block, but it looks like the special handling for ServiceUnavailableException is missing for XML requests. What do you think?

[oleua]

So, the fix for 32.0.5 hasn't worked.

[no app in context] Помилка: Uncaught exception
	PROPFIND /remote.php/dav/files/username	/

{"reqId":"GAclXYcuFyb9TPjVTjXE","level":3,"time":"2026-02-05T02:31:15+02:00","remoteAddr":"****","user":"--","app":"no app in context","method":"PROPFIND","url":"/remote.php/dav/files/username/","scriptName":"/remote.php","message":"Uncaught exception","userAgent":"rclone/v1.73.0","version":"32.0.5.0","exception":{"Exception":"OCA\\DAV\\Exception\\ServerMaintenanceMode","Message":"Система в режимі обслуговування.","Code":0,"Trace":[{"file":"/www/html/nextcloud/3rdparty/sabre/event/lib/WildcardEmitterTrait.php","line":89,"function":"checkMaintenanceMode","class":"OCA\\DAV\\Connector\\Sabre\\MaintenancePlugin","type":"->"},{"file":"/www/html/nextcloud/3rdparty/sabre/dav/lib/DAV/Server.php","line":456,"function":"emit","class":"Sabre\\DAV\\Server","type":"->"},{"file":"/www/html/nextcloud/apps/dav/lib/Connector/Sabre/Server.php","line":211,"function":"invokeMethod","class":"Sabre\\DAV\\Server","type":"->"},{"file":"/www/html/nextcloud/apps/dav/lib/Server.php","line":425,"function":"start","class":"OCA\\DAV\\Connector\\Sabre\\Server","type":"->"},{"file":"/www/html/nextcloud/apps/dav/appinfo/v2/remote.php","line":22,"function":"exec","class":"OCA\\DAV\\Server","type":"->"},{"file":"/www/html/nextcloud/remote.php","line":151,"args":["/www/html/nextcloud/apps/dav/appinfo/v2/remote.php"],"function":"require_once"}],"File":"/www/html/nextcloud/apps/dav/lib/Connector/Sabre/MaintenancePlugin.php","Line":65,"message":"Uncaught exception","exception":[],"CustomMessage":"Uncaught exception"},"id":"****"}