CI: add a way to set up dbus notifications in test environment(#130)

this modifies the workflow file to add the following packages:

* dunst: the notification daemon
* xvfb: virtual framebuffer x11 server, needed because dunst has to connect to x11 to display a notification graphically and I can't find a proper headless one

it then proceeds to create a dbus user session and a system one, to finally run dunst in the background, ready to recieve a notification, from other tests perhaps

.github/workflows/ci.yml

@@ -39,7 +39,12 @@ jobs:
           target: ${{ matrix.target }}
 
       - name: Install Dependencies
-        run: sudo apt -y install at-spi2-core systemd
+        run: sudo apt -y install at-spi2-core systemd dunst xvfb
+      - name: setup dbus and notification daemon
+        run:
+          sudo systemctl start dbus;
+          systemctl --user start dbus;
+          xvfb-run dunst --screen 0 600x400x8 &
       - name: Run tests
         run: cargo test
   clippy: