🏷️(CI) add automated label to renovate

Renovate provides automated pull requests, so let's
use a label to identify them easily.

renovate.json

@@ -1,7 +1,7 @@
 {
   "extends": ["github>numerique-gouv/renovate-configuration"],
   "dependencyDashboard": true,
-  "labels": ["dependencies", "noChangeLog"],
+  "labels": ["dependencies", "noChangeLog", "automated"],
   "packageRules": [
     {
       "enabled": false,