Configure Renovate to update uv.lock unpinned dependencies (#832)

As discussed in `uv` PR:

* `uv.lock` pins the git commit hashes used when pulling `django-stubs`/`django-stubs-ext`. But if there's an incompatible change in there, we want to know of it.
* Configured Renovate to update these daily (we'll see, maybe that's too frequent).
* If the "test" GitHub workflow passes, Renovate will auto-merge. Otherwise it will open a PR.

Author: intgr

.github/renovate.json

@@ -0,0 +1,14 @@
+{
+  "dependencyDashboard": false,
+  "lockFileMaintenance": {
+    "enabled": true,
+    "schedule": ["* 3-4 * * *"],
+    "automerge": true,
+    "automergeType": "branch"
+  },
+  "packageRules": [
+    {
+      "enabled": false
+    }
+  ]
+}

.github/workflows/test.yml

@@ -4,6 +4,7 @@ on:
   push:
     branches:
       - master
+      - "renovate/**"
   pull_request:
   workflow_dispatch:
   schedule: