spice-vdagent: 0.17.0 -> 0.18.0 (#42204)

Semi-automatic update generated by https://github.com/ryantm/nixpkgs-update tools.

This update was made based on information from https://repology.org/metapackage/spice-vdagent/versions.

These checks were done:

- built on NixOS
- /nix/store/jn5icaw3pkbvyh2j34lqnx8w1ikqj7k2-spice-vdagent-0.18.0/bin/spice-vdagent passed the binary check.
- /nix/store/jn5icaw3pkbvyh2j34lqnx8w1ikqj7k2-spice-vdagent-0.18.0/bin/spice-vdagentd passed the binary check.
- 2 of 2 passed binary check by having a zero exit code.
- 0 of 2 passed binary check by having the new version present in output.
- found 0.18.0 with grep in /nix/store/jn5icaw3pkbvyh2j34lqnx8w1ikqj7k2-spice-vdagent-0.18.0
- directory tree listing: https://gist.github.com/b66bf12f870f109e97e063ee890be440
- du listing: https://gist.github.com/6bd67c42fafb9c4b45a004edcf1807fb