Bump org.springframework.boot in /subscription-example

Bumps [org.springframework.boot](https://github.com/spring-projects/spring-boot) from 3.1.0 to 3.1.2.
- [Release notes](https://github.com/spring-projects/spring-boot/releases)
- [Commits](spring-projects/spring-boot@v3.1.0...v3.1.2)

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

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

subscription-example/build.gradle

@@ -1,5 +1,5 @@
 plugins {
-	id 'org.springframework.boot' version '3.1.0'
+	id 'org.springframework.boot' version '3.1.2'
 	id 'io.spring.dependency-management' version '1.1.0'
 	id 'java'
 }