Tweak PR build script

Author: rbuckton

.github/workflows/pr.yml

@@ -5,7 +5,10 @@ on:
 jobs:
   build:
     runs-on: ubuntu-latest
-    permissions: write-all
+    permissions:
+      pull-requests: write
+      contents: write
+      pages: write
     if: ${{ github.event.number }}
     steps:
       - uses: actions/checkout@v4