share_folder can be shared

[HanaGemela]

Server: 10.3.0RC1

Steps to recreate:

1. Add share_folder into config.php
2. User1 shares a file with User2
3. User2 deletes the file from their account
4. User2 shares share_folder

Actual result: share_folder can be shared. Any new files which are added to that folder as newly received shares are not shared to the collaborators. But new files can be added via public links. This is confusing

Expected result: Sharing of share_folder is not allowed

[phil-davis]

I expect that users have been able to do this sort of thing in all core versions (since whenever share_folder was introduced)

So IMO this is not a regression, but it is a good idea to prevent users sharing the special folder share_folder

[karakayasemi]

share permission is removed for share_folder and its parent folders by #36337.