chore: add github actions to renovate config (#144)

Allow renovate to update the GitHub workflows.

Signed-off-by: Francesco Canovai <francesco.canovai@enterprisedb.com>

renovate.json

@@ -1,7 +1,10 @@
 {
   "$schema": "https://docs.renovatebot.com/renovate-schema.json",
   "extends": ["config:recommended", "docker:pinDigests"],
-  "enabledManagers": ["custom.regex"],
+  "enabledManagers": [
+    "github-actions",
+    "custom.regex"
+  ],
   "customManagers": [
     {
       "customType": "regex",