Update Flatpak build workflow for new image and actions

.github/workflows/flatpak-build.yml

@@ -1,24 +1,25 @@
 name: Flatpak Build
+
 on:
   push:
-    branches:
-      - master
+    branches: [master]
   pull_request:
-    branches:
-      - master
+    branches: [master]
 
 jobs:
   flatpak_build:
     runs-on: ubuntu-latest
     container:
-      image: bilelmoussaoui/flatpak-github-actions:gnome-46
+      image: ghcr.io/flathub-infra/flatpak-github-actions:gnome-49
       options: --privileged
-    steps:
-    - uses: actions/checkout@v2
-      with:
-        submodules: true
 
-    - uses: bilelmoussaoui/flatpak-github-actions/flatpak-builder@v3
-      with:
-        bundle: zoitechat.flatpak
-        manifest-path: flatpak/io.github.Zoitechat.json
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          submodules: true
+
+      - uses: flatpak/flatpak-github-actions/flatpak-builder@v6
+        with:
+          bundle: zoitechat.flatpak
+          manifest-path: flatpak/io.github.Zoitechat.json
+          cache-key: flatpak-builder-${{ github.sha }}