Fix permissions to publish GitHub pages.

.github/workflows/generate_github_pages.yml

@@ -12,6 +12,8 @@ jobs:
     runs-on: ubuntu-latest
     # Skip in forks
     if: ${{ github.event_name != 'pull_request' || github.event.pull_request.head.repo.full_name == 'element-hq/element-x-android' }}
+    permissions:
+      contents: write
     steps:
       - name: ⏬ Checkout with LFS
         uses: nschloe/action-cached-lfs-checkout@1c185ad576953eab13e35ffe1bffef437d97e9d2 # v1.2.4