alter workflow to use v3

.gitea/workflows/site.yml

@@ -13,7 +13,7 @@ jobs:
     runs-on: build
 
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v3
 
       - name: Install
         run: npm ci --ignore-scripts --no-audit --no-fund
@@ -42,7 +42,7 @@ jobs:
         shell: bash
 
     steps:
-      - uses: actions/download-artifact@v4
+      - uses: actions/download-artifact@v3
         with:
           name: site
           path: _site