Bump org.springframework.boot from 3.3.4 to 3.5.6 in /giftcard-example

Bumps [org.springframework.boot](https://github.com/spring-projects/spring-boot) from 3.3.4 to 3.5.6.
- [Release notes](https://github.com/spring-projects/spring-boot/releases)
- [Commits](spring-projects/spring-boot@v3.3.4...v3.5.6)

---
updated-dependencies:
- dependency-name: org.springframework.boot
  dependency-version: 3.5.6
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

giftcard-example/build.gradle

@@ -1,5 +1,5 @@
 plugins {
-    id 'org.springframework.boot' version '3.3.4'
+    id 'org.springframework.boot' version '3.5.6'
     id 'io.spring.dependency-management' version '1.1.7'
 
     id 'java'