lint: Require dangling comma in multi-line imports

This keeps the config in line with gjs, which added the option
in gjs@f7d3b5d4c8.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell-extensions/-/merge_requests/411>
(cherry picked from commit 301017904b)

lint/eslintrc-gjs.yml

@@ -30,6 +30,7 @@ rules:
     - error
     - arrays: always-multiline
       objects: always-multiline
+      imports: always-multiline
       functions: never
   comma-spacing:
     - error