chore(deps): update plugin org.springframework.boot to v3.5.9

Author: renovate[bot]

build.gradle

@@ -1,7 +1,7 @@
 plugins {
     // Spring boot & dependency management:
     // https://docs.spring.io/spring-boot/docs/current/gradle-plugin/reference/htmlsingle/
-    id 'org.springframework.boot' version '3.5.5'
+    id 'org.springframework.boot' version '3.5.9'
     // https://docs.spring.io/dependency-management-plugin/docs/current-SNAPSHOT/reference/html/
     id "io.spring.dependency-management" version "1.1.7"
     // Lombok generates getter and setter and more. https://projectlombok.org/