Bump plugin.spring from 1.7.20 to 1.7.21

Bumps [plugin.spring](https://github.com/JetBrains/kotlin) from 1.7.20 to 1.7.21.
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](https://github.com/JetBrains/kotlin/commits)

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

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

build.gradle.kts

@@ -4,7 +4,7 @@ plugins {
     id("org.springframework.boot") version "2.7.5" apply false
     id("io.spring.dependency-management") version "1.1.0" apply false
     kotlin("jvm") version "1.7.21" apply false
-    kotlin("plugin.spring") version "1.7.20" apply false
+    kotlin("plugin.spring") version "1.7.21" apply false
     kotlin("plugin.jpa") version "1.7.21" apply false
 }