Update kotlinx.serialization badge version

Author: BenWoodworth

README.md

@@ -4,7 +4,7 @@
 [![Maven Snapshots](https://img.shields.io/maven-metadata/v?label=maven-snapshots&metadataUrl=https%3A%2F%2Fcentral.sonatype.com%2Frepository%2Fmaven-snapshots%2Fnet%2Fbenwoodworth%2Fknbt%2Fknbt%2Fmaven-metadata.xml)](https://central.sonatype.com/service/rest/repository/browse/maven-snapshots/net/benwoodworth/knbt/knbt)
 [![KDoc](https://img.shields.io/badge/api-KDoc-blue)](https://benwoodworth.github.io/knbt)
 [![Kotlin](https://img.shields.io/badge/kotlin-2.2.21-blue.svg?logo=kotlin)](http://kotlinlang.org)
-[![kotlinx.serialization](https://img.shields.io/badge/kotlinx.serialization-1.8.0-blue.svg?logo=kotlin)](https://github.com/Kotlin/kotlinx.serialization)
+[![kotlinx.serialization](https://img.shields.io/badge/kotlinx.serialization-1.9.0-blue.svg?logo=kotlin)](https://github.com/Kotlin/kotlinx.serialization)
 
 An implementation of [Minecraft's NBT format](https://minecraft.wiki/w/NBT_format)
 for [kotlinx.serialization](https://github.com/Kotlin/kotlinx.serialization).