Use internal renovate config.

Inspired by @jkempster34:

The internal renovate config automatically merges minor updates compared to the
standard configuration which only merges patches.

As we struggle to keep on top of renovate merges in this repo, I propose we use
the internal config here for minor updates.

renovate.json

@@ -1,4 +1,4 @@
 {
   "$schema": "https://docs.renovatebot.com/renovate-schema.json",
-  "extends": ["github>dxw/renovate-config"]
+  "extends": ["github>dxw/renovate-config:internal"]
 }