Bump plugin.allopen from 1.9.20 to 1.9.21 in /quarkus-app (#69)

Bumps [plugin.allopen](https://github.com/JetBrains/kotlin) from 1.9.20 to 1.9.21.
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](JetBrains/kotlin@v1.9.20...v1.9.21)

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

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

quarkus-app/build.gradle.kts

@@ -1,6 +1,6 @@
 plugins {
     kotlin("jvm") version "1.9.21"
-    kotlin("plugin.allopen") version "1.9.20"
+    kotlin("plugin.allopen") version "1.9.21"
     id("io.quarkus")
 }