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

zita-convolver: add fftw-devel dependency to zita-convolver-devel
https://github.com/void-linux/void-packages/pull/31666

Description:
<!-- Mark items with [x] where applicable -->

Without this change the packages which depend on `zita-convolver-devel` fail to compile due to missing `ftw3.h` header.

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

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