Bump serialization from 1.8.1 to 1.9.0

Bumps `serialization` from 1.8.1 to 1.9.0.

Updates `org.jetbrains.kotlinx:kotlinx-serialization-json` from 1.8.1 to 1.9.0
- [Release notes](https://github.com/Kotlin/kotlinx.serialization/releases)
- [Changelog](https://github.com/Kotlin/kotlinx.serialization/blob/master/CHANGELOG.md)
- [Commits](Kotlin/kotlinx.serialization@v1.8.1...v1.9.0)

Updates `org.jetbrains.kotlinx:kotlinx-serialization-json-okio` from 1.8.1 to 1.9.0
- [Release notes](https://github.com/Kotlin/kotlinx.serialization/releases)
- [Changelog](https://github.com/Kotlin/kotlinx.serialization/blob/master/CHANGELOG.md)
- [Commits](Kotlin/kotlinx.serialization@v1.8.1...v1.9.0)

---
updated-dependencies:
- dependency-name: org.jetbrains.kotlinx:kotlinx-serialization-json
  dependency-version: 1.9.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
- dependency-name: org.jetbrains.kotlinx:kotlinx-serialization-json-okio
  dependency-version: 1.9.0
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

gradle/libs.versions.toml

@@ -4,7 +4,7 @@ kotest = "6.0.0.M3"
 detekt = "1.23.8"
 ktlint = "1.1.0"
 okio = "3.15.0"
-serialization = "1.8.1"
+serialization = "1.9.0"
 benchmark = "0.4.14"
 openapi = "2025.3"
 jackson = "2.19.2"