Pin Spring Boot version

RISDEV-8001
Is not compatible with spring-cloud-kubernetes, see spring-cloud/spring-cloud-kubernetes#1923

Author: kiwikern

renovate.json5

@@ -21,7 +21,12 @@
     "after 7:30pm every weekday"
   ],
   "automergeType": "pr",
+  // FIXME: Remove this when spring-cloud-kubernetes is compatible, see https://github.com/spring-cloud/spring-cloud-kubernetes/issues/1923
   "packageRules": [
+    {
+      "matchPackageNames": ['org.springframework.boot'],
+      "allowedVersions": "3.4.x"
+    },
     {
       "groupName": "all-frontend-non-major-dependencies",
       "matchPaths": [