chore(renovate): ignore go.opentelemetry.io/otel/sdk/log/logtest (#6501)

In order not to have PRs like these:
- https://github.com/open-telemetry/opentelemetry-go/pull/6478
- https://github.com/open-telemetry/opentelemetry-go/pull/6477

Renovate docs:
https://docs.renovatebot.com/configuration-options/#enabled

renovate.json

@@ -25,6 +25,10 @@
     {
       "matchPackageNames": ["golang.org/x/**"],
       "groupName": "golang.org/x"
+    },
+    {
+      "matchPackageNames": ["go.opentelemetry.io/otel/sdk/log/logtest"],
+      "enabled": false
     }
   ]
 }