2543: Fix#2231: make public announcements work r=nextgens a=nextgens
## What type of PR?
bug-fix
## What does this PR do?
Ensure public announcements bypass filters.
They can still time-out... but this is already a big improvement that we should be able to backport.
### Related issue(s)
- closes#2231
## Prerequisites
Before we can consider review and merge, please make sure the following list is done and checked.
If an entry in not applicable, you can check it or remove it from the list.
- [ ] In case of feature or enhancement: documentation updated accordingly
- [x] Unless it's docs or a minor change: add [changelog](https://mailu.io/master/contributors/workflow.html#changelog) entry file.
Co-authored-by: Florent Daigniere <nextgens@freenetproject.org>
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