chore: limit concurrent renovate PRs

There are just too many dependencies to update. So limit to have only 5 PRs open at any one time.

Author: JP-Ellis

.github/renovate.json

@@ -2,6 +2,6 @@
   "$schema": "https://docs.renovatebot.com/renovate-schema.json",
   "extends": ["config:best-practices"],
   "prHourlyLimit": 0,
-  "prConcurrentLimit": 0,
+  "prConcurrentLimit": 5,
   "automerge": true
-}
+}