Bump io.spring.dependency-management from 1.1.5 to 1.1.6 in /backend

Bumps [io.spring.dependency-management](https://github.com/spring-gradle-plugins/dependency-management-plugin) from 1.1.5 to 1.1.6.
- [Release notes](https://github.com/spring-gradle-plugins/dependency-management-plugin/releases)
- [Commits](spring-gradle-plugins/dependency-management-plugin@v1.1.5...v1.1.6)

---
updated-dependencies:
- dependency-name: io.spring.dependency-management
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

backend/build.gradle

@@ -1,7 +1,7 @@
 plugins {
     id 'org.springframework.boot' version '3.1.7'
     id 'org.liquibase.gradle' version '2.2.2'
-    id 'io.spring.dependency-management' version '1.1.5'
+    id 'io.spring.dependency-management' version '1.1.6'
     id 'java'
     id 'checkstyle'
     id 'jacoco'