fix(publish.yml): change ubuntu version

.github/workflows/publish.yaml

@@ -1,17 +1,22 @@
 name: Publish to GitHub Pages
 
 on:
-  push:
+  # JUST FOR TESTING
+  # push:
+  #   branches:
+  #     - main
+  pull_request:
     branches:
       - main
   workflow_dispatch:
 
 env:
   FLUTTER_VERSION: 3.16.5
+  UBUNTU_IMAGE: ubuntu-22.04
 
 jobs:
   publish:
-    runs-on: ubuntu-latest
+    runs-on: $UBUNTU_IMAGE
     steps:
       - uses: actions/checkout@v2
       - uses: subosito/flutter-action@v2