Bump plugin.spring in /projects/spring-ai/playground-flight-booking

Bumps [plugin.spring](https://github.com/JetBrains/kotlin) from 2.1.21 to 2.2.21.
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](JetBrains/kotlin@v2.1.21...v2.2.21)

---
updated-dependencies:
- dependency-name: plugin.spring
  dependency-version: 2.2.21
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

projects/spring-ai/playground-flight-booking/build.gradle.kts

@@ -1,6 +1,6 @@
 plugins {
     kotlin("jvm") version "2.2.21"
-    kotlin("plugin.spring") version "2.1.21"
+    kotlin("plugin.spring") version "2.2.21"
     id("org.springframework.boot") version "4.0.0"
     id("io.spring.dependency-management") version "1.1.7"
     id("com.vaadin") version "24.9.6"