/backport to stable31

From #618 (comment) and https://docs.nextcloud.com/server/latest/admin_manual/apps_management.html#using-custom-app-directories,
it seems like apps_path is always supposed to be an array but it wasn't in the linked issue so it was a config issue. That may have been fixed with just setting the writable key to true.
in the PR we might write to apps directory that are not supposed to be written. That should be an error as it was imo.

From #618 (comment) and https://docs.nextcloud.com/server/latest/admin_manual/apps_management.html#using-custom-app-directories, it seems like apps_path is always supposed to be an array but it wasn't in the linked issue so it was a config issue. That may have been fixed with just setting the writable key to true. in the PR we might write to apps directory that are not supposed to be written. That should be an error as it was imo.

I agree, lets then keep it as it was, since it is supposed to work with apps_paths that is common recommended way of configuration.

sorry I was mistaken with the apps_paths config key. It is an optional key and the fallback implemented here is correct: https://github.com/nextcloud/server/blob/083f0b51dd6740dc6973f9d3ec1f95719a1d7d0e/lib/base.php#L152-L164

/backport to stable32