There's a merged pull request on the void-packages repository

ImageMagick6: update to 6.9.12.1
https://github.com/void-linux/void-packages/pull/29101

Description:
#### General
- [ ] This is a new package and it conforms to the [quality requirements](https://github.com/void-linux/void-packages/blob/master/Manual.md#quality-requirements)

#### Have the results of the proposed changes been tested?
- [ ] I use the packages affected by the proposed changes on a regular basis and confirm this PR works for me
- [x] I generally don't use the affected packages but briefly tested this PR

No revbumps needed as there are no consumers of libMagick++-6.Q16.so.9