Update flatpak-github-actions to v4 (#67)

Author: dar5hak

.github/workflows/ci.yml

@@ -25,7 +25,7 @@ jobs:
         uses: actions/checkout@v2
 
       - name: Build
-        uses: bilelmoussaoui/flatpak-github-actions/flatpak-builder@v3
+        uses: bilelmoussaoui/flatpak-github-actions/flatpak-builder@v4
         with:
           bundle: badger.flatpak
           manifest-path: com.github.elfenware.badger.yml