fix(deps): update spring boot to v4

Author: elastic-renovate-prod[bot]

smoke-tests/test-app/build.gradle.kts

@@ -14,7 +14,7 @@ dependencies {
   // - http endpoint, which is easy to call remotely
   // - implement a server, which is not a single invocation only like a CLI app
   // - multiple endpoints are possible, which allows multiple test scenarios
-  val springBootVersion = "2.7.18";
+  val springBootVersion = "4.0.1";
   testImplementation("org.springframework.boot:spring-boot-starter-test:${springBootVersion}")
   implementation("org.springframework.boot:spring-boot-starter-web:${springBootVersion}")