feat: require caldav backend #5955

Job	Run time
php8.1 on master integration tests	1m 38s
php8.1 on master unit tests	1m 58s
php8.1 on stable29 integration tests	1m 31s
php8.1 on stable29 unit tests	1m 40s
php8.2 on master integration tests	3m 16s
php8.2 on master unit tests	3m 45s
php8.2 on stable29 integration tests	3m 38s
php8.2 on stable29 unit tests	3m 49s
php8.3 on master integration tests	3m 8s
php8.3 on master unit tests	3m 18s
php8.3 on stable29 integration tests	2m 34s
php8.3 on stable29 unit tests	2m 43s
php8.0 on stable27 integration tests	3m 26s
php8.0 on stable27 unit tests	3m 21s
php8.1 on stable28 integration tests	1m 52s
php8.1 on stable28 unit tests	1m 34s
php-test-summary	7s
	43m 18s

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