Gradle: Bump org.springframework.boot from 3.5.8 to 4.0.0

Bumps [org.springframework.boot](https://github.com/spring-projects/spring-boot) from 3.5.8 to 4.0.0.
- [Release notes](https://github.com/spring-projects/spring-boot/releases)
- [Commits](spring-projects/spring-boot@v3.5.8...v4.0.0)

---
updated-dependencies:
- dependency-name: org.springframework.boot
  dependency-version: 4.0.0
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

build.gradle.kts

@@ -31,7 +31,7 @@ plugins {
   kotlin("plugin.spring") version kotlinVersion apply false
   id("pl.allegro.tech.build.axion-release") version "1.21.1"
   id("com.diffplug.spotless") version "8.1.0"
-  id("org.springframework.boot") version "3.5.8" apply false
+  id("org.springframework.boot") version "4.0.0" apply false
   id("project-report")
   id("org.owasp.dependencycheck") version "12.1.9"
   id("com.github.jk1.dependency-license-report") version "3.0.1"