control: Use Granite 9

[ryonakano]

Followup #682

I confirmed I can build #682 with the following commands:

$ docker run --rm -it ghcr.io/elementary/docker:development-target bash

(inside docker)
# git clone https://github.com/elementary/wingpanel.git
# cd wingpanel/
# git checkout danirabbit/granite-9
# git checkout origin/ryonakano/deb-packaging-granite-9 -- debian
# apt build-dep .
# meson setup builddir --prefix=/usr
# meson compile -C builddir