github: fix invalid permission settings for docs workflow

Similar to #5792. We haven't had any updates to the GitHub pages since
#5076, AFAICT.

.github/workflows/docs.yml

@@ -9,6 +9,8 @@ permissions: {}
 
 jobs:
   prerelease-docs-build-deploy:
+    permissions:
+      contents: write
     if: github.repository_owner == 'jj-vcs' # Stops this job from running on forks
     strategy:
       matrix:
@@ -18,7 +20,7 @@ jobs:
     steps:
       - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
         with:
-          persist-credentials: false          
+          persist-credentials: false
       - run:  "git fetch origin gh-pages --depth=1"
       - uses: actions/setup-python@42375524e23c412d93fb67b49958b491fce71c38
         with:
@@ -28,8 +30,6 @@ jobs:
         with:
           version: "0.5.1"
       - name: Install dependencies, compile and deploy docs
-        permissions:
-          contents: write
         run: |
           git config user.name 'jj-docs[bot]'
           git config user.email 'jj-docs[bot]@users.noreply.github.io'