Bump org.springframework.boot from 3.3.5 to 3.4.2 in /backend

Bumps [org.springframework.boot](https://github.com/spring-projects/spring-boot) from 3.3.5 to 3.4.2.
- [Release notes](https://github.com/spring-projects/spring-boot/releases)
- [Commits](spring-projects/spring-boot@v3.3.5...v3.4.2)

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

Signed-off-by: dependabot[bot] <support@github.com>

backend/build.gradle

@@ -1,5 +1,5 @@
 plugins {
-	id 'org.springframework.boot' version '3.3.5'
+	id 'org.springframework.boot' version '3.4.2'
 	id 'io.spring.dependency-management' version '1.1.7'
 	id 'java'
 	id 'jacoco'