flatpak: Add test-args

This should fix several failures when running the test suite in our
Flatpak build, as they are not able to reach the Wayland compositor.

org.gnome.Geary.json

@@ -272,6 +272,16 @@
         {
             "name": "geary",
             "buildsystem": "meson",
+            "build-options": {
+                "test-args": [
+                    "--share=ipc",
+                    "--socket=x11",
+                    "--socket=wayland",
+                    "--device=dri",
+                    "--socket=pulseaudio",
+                    "--share=network"
+                ]
+            },
             "config-opts": [
                 "-Dprofile=development"
             ],