ci: Bump flatpak-github-actions to 49

Author: hbons

.github/workflows/flatpak.yml

@@ -8,7 +8,7 @@ jobs:
   flatpak:
     name: "Flatpak"
     container:
-      image: ghcr.io/flathub-infra/flatpak-github-actions:gnome-48
+      image: ghcr.io/flathub-infra/flatpak-github-actions:gnome-49
       options: --privileged
     strategy:
       matrix: