deps: update spring-boot.version to v3.5.9 (GoogleCloudPlatform#4053)

Author: renovate-bot

samples/cloud-run/java/pom.xml

@@ -21,7 +21,7 @@
     <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
     <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
 
-    <spring-boot.version>3.5.8</spring-boot.version>
+    <spring-boot.version>3.5.9</spring-boot.version>
     <junixsocket.version>2.10.1</junixsocket.version>
   </properties>