ci(renovate): manage actions (#13)

As this repo has actions, we want renovate to manage those as well.

Reviewed-on: #13
Co-authored-by: t.behrendt <t.behrendt@t00n.de>
Co-committed-by: t.behrendt <t.behrendt@t00n.de>

renovate.json

@@ -1,6 +1,7 @@
 {
   "$schema": "https://docs.renovatebot.com/renovate-schema.json",
   "extends": [
-    "local>t.behrendt/renovate-configs:common"
+    "local>t.behrendt/renovate-configs:common",
+    "local>t.behrendt/renovate-configs:action"
   ]
 }