Switch to checkout@v3

Author: mpe

.github/workflows/deploy.yml

@@ -20,7 +20,7 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v2
+        uses: actions/checkout@v3
 
       - name: Build docker image
         run: make -C build rebuild-image@$SUBARCH@$IMAGE