Bump plugin.serialization from 2.0.0 to 2.0.20 in /api (#25)

Bumps [plugin.serialization](https://github.com/JetBrains/kotlin) from 2.0.0 to 2.0.20.
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](JetBrains/kotlin@v2.0.0...v2.0.20)

---
updated-dependencies:
- dependency-name: plugin.serialization
  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>

api/app/build.gradle.kts

@@ -6,7 +6,7 @@ import org.gradle.api.tasks.testing.logging.TestLogEvent
 
 plugins {
  kotlin("jvm") version "2.0.20"
- kotlin("plugin.serialization") version "2.0.0"
+ kotlin("plugin.serialization") version "2.0.20"
  id("io.ktor.plugin") version "3.0.0-beta-2"
  id("com.github.johnrengelman.shadow") version "8.1.1"
  id("org.jlleitschuh.gradle.ktlint") version "12.1.1"