forgejo-ci: use checkout action to fetch public

.forgejo/workflows/pages.yaml

@@ -13,8 +13,12 @@ jobs:
         uses: actions/checkout@v4
         with:
           fetch-depth: 500
-      - name: Clones public branch
-        run: git clone ./ -b public public
+      - name: Public repo pull
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 500
+          ref: public
+          path: public
       - name: Render website
         run: ikiwiki --setup ikiwiki.setup
       - name: Website upload