Group share accepting/rejecting keeps re-triggering notifications for others

[wiswedel]

regarding #16828

Steps to reproduce

• Alice and Bob are members of group foo
• Trudy shares a file with group foo
• Alice gets a notification about the incoming group share
• Bob gets a notification about the incoming group share
• Alice accepts the share
• Bob rejects the share

Expected behaviour

• nothing more, everyone reacted

Actual behaviour

• Alice gets the same notification again about the incoming group share she already accepted earlier

side note

This happens no matter if Bob rejects or accepts the share.

[skjnldsv]

Please use appropriate labels

[rullzer]

Fix in #18294