Update kotlinx.serialization to v1.8.1

| datasource | package                                          | from  | to    |
| ---------- | ------------------------------------------------ | ----- | ----- |
| maven      | org.jetbrains.kotlinx:kotlinx-serialization-core | 1.6.3 | 1.8.1 |
| maven      | org.jetbrains.kotlinx:kotlinx-serialization-json | 1.6.3 | 1.8.1 |

Author: renovate[bot]

gradle/libs.versions.toml

@@ -5,7 +5,7 @@ kotlinx-collections-immutable = "0.3.8"
 kotlinx-coroutines = "1.9.0"
 kotlinx-atomicfu = "0.26.0"
 kotlinx-datetime = "0.6.1"
-kotlinx-serialization = "1.6.3"
+kotlinx-serialization = "1.8.1"
 
 jetbrains-compose-mutiplatform = "1.5.12"