Update actions/checkout to v3 in themes-weekly-pull.yml

Co-authored-by: per1234 <accounts@perglass.com>

Author: francescospissu

.github/workflows/themes-weekly-pull.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
 
       - name: Install Node.js 14.x
         uses: actions/setup-node@v2