Let snap-store snap refresh while the app is running Fixes #1643

This will require a snapcraft built after
canonical/snapcraft#4749 has been merged to
build.

snap/snapcraft.yaml

@@ -5,6 +5,7 @@ confinement: strict
 base: core22
 grade: stable
 version: git
+assumes: [snapd2.57] # Needed for ignore-running refresh-mode
 
 parts:
   flutter-git:
@@ -57,6 +58,7 @@ apps:
       RATINGS_SERVICE_URL: 'ratings.ubuntu.com'
     desktop: bin/data/flutter_assets/assets/app-center.desktop
     extensions: [gnome]
+    refresh-mode: ignore-running
     plugs:
       - appstream-metadata
       - desktop