Normalise the JSON redirects file before diffing

This ensures that key-ordering changes, which don't affect the
semantics of the file, don't create diff noise.

.github/workflows/publish.yml

@@ -115,6 +115,18 @@ jobs:
           name: build-from-main
           path: main
 
+      - name: Normalise JSON
+        shell: python
+        run: |
+          import json
+          from pathlib import Path
+
+          p = Path('_site') / 'redirects.json'
+          p.write_text(json.dumps(
+              json.loads(p.read_text()),
+              sort_keys=True,
+          ))
+
       - name: Diff
         id: diff
         run: |