chore: bump plugin.spring from 2.1.20 to 2.1.21 in /dgs-subscription-ws (#3288)

Bumps [plugin.spring](https://github.com/JetBrains/kotlin) from 2.1.20 to 2.1.21.
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](JetBrains/kotlin@v2.1.20...v2.1.21)

---
updated-dependencies:
- dependency-name: plugin.spring
  dependency-version: 2.1.21
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

dgs-subscription-ws/build.gradle.kts

@@ -6,7 +6,7 @@ plugins {
     id("io.spring.dependency-management") version "1.1.7"
 
     kotlin("jvm") version "2.1.20"
-    kotlin("plugin.spring") version "2.1.20"
+    kotlin("plugin.spring") version "2.1.21"
     id("com.netflix.dgs.codegen") version "8.0.2" //https://plugins.gradle.org/plugin/com.netflix.dgs.codegen
 }