Bump plugin.spring from 1.8.22 to 1.9.20 in /service

Bumps [plugin.spring](https://github.com/JetBrains/kotlin) from 1.8.22 to 1.9.20.
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](JetBrains/kotlin@v1.8.22...v1.9.20)

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

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

service/build.gradle.kts

@@ -4,7 +4,7 @@ plugins {
     id("org.springframework.boot") version "3.1.5"
     id("io.spring.dependency-management") version "1.1.3"
     kotlin("jvm") version "1.8.22"
-    kotlin("plugin.spring") version "1.8.22"
+    kotlin("plugin.spring") version "1.9.20"
     id("org.flywaydb.flyway") version "9.19.4"
     id("org.jlleitschuh.gradle.ktlint") version "11.6.1"
 }