synthv1: 0.8.6 -> 0.9.0

Semi-automatic update generated by https://github.com/ryantm/nix-update tools. These checks were done:

- built on NixOS
- Warning: no binary found that responded to help or version flags. (This warning appears even if the package isn't expected to have binaries.)
- found 0.9.0 with grep in /nix/store/xn775251xcr8bnkpzqwicv0sq0fv2nb3-synthv1-0.9.0
- found 0.9.0 in filename of file in /nix/store/xn775251xcr8bnkpzqwicv0sq0fv2nb3-synthv1-0.9.0