[ci] Remove nested container to avoid bwrap namespace issues

.gitea/workflows/build-flatpak.yml

@@ -11,14 +11,16 @@ jobs:
   flatpak:
     name: Build Flatpak
     runs-on: ubuntu-latest
-    container:
-      image: bilelmoussaoui/flatpak-github-actions:gnome-nightly
-      options: --privileged --device=/dev/fuse
 
     steps:
       - name: Checkout Code
         run: git clone --depth 1 http://gitea.service:3000/secstate/Notify.git .
 
+      - name: Install Flatpak Tools
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y flatpak flatpak-builder
+
       - name: Add Flathub
         run: flatpak --user remote-add --if-not-exists flathub https://flathub.org/repo/flathub.flatpakrepo