renovate: add package rule for pretalx reclassifying major updates

So that v2025.1.0 to v2025.2.2 counts as a major, not a minor, update.

renovate.json

@@ -32,6 +32,11 @@
       "matchDatasources": ["docker"],
       "matchPackageNames": ["docker.io/pretix/standalone"],
       "versioning": "regex:^(?<major>\\d+\\.\\d+)(?:\\.(?<minor>\\d+))$"
+    },
+    {
+      "matchDatasources": ["docker"],
+      "matchPackageNames": ["docker.io/pretalx/standalone"],
+      "versioning": "regex:^v(?<major>\\d+\\.\\d+)(?:\\.(?<minor>\\d+))$"
     }
   ],
   "customManagers": [