ci: Update permissions for github-pages workflow

amalgamate-pages@v2 requires pull-requests: write to post PR comments.

I intend to also add the ability to set the build status so I am
preëmptively adding that permission too.

Author: wjt

.github/workflows/github-pages.yml

@@ -15,6 +15,8 @@ permissions:
   contents: read
   pages: write
   id-token: write
+  pull-requests: write
+  statuses: write
 
 jobs:
   publish: