ci: disable test.pypi.org in hostRules for Renovate configuration (#267)

This pull request makes a small configuration update to the Renovate bot
settings. Specifically, it disables Renovate for the PyPI test
repository by adding a new host rule.

- Renovate configuration: Added a rule to disable Renovate for the
`test.pypi.org` PyPI host in `.github/renovate.json`.

Author: a-klos

.github/renovate.json

@@ -12,6 +12,11 @@
   "stabilityDays": 7,
   "repositories": ["stackitcloud/rag-template"],
   "hostRules": [
+    {
+      "hostType": "pypi",
+      "matchHost": "test.pypi.org",
+      "enabled": false
+    },
     {
       "hostType": "docker",
       "matchHost": "ghcr.io"