build(deps): bump kotlinVersion from 2.0.21 to 2.1.0 in /webinterface

Bumps `kotlinVersion` from 2.0.21 to 2.1.0.

Updates `plugin.serialization` from 2.0.21 to 2.1.0
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/v2.1.0/ChangeLog.md)
- [Commits](JetBrains/kotlin@v2.0.21...v2.1.0)

Updates `multiplatform` from 2.0.21 to 2.1.0
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/v2.1.0/ChangeLog.md)
- [Commits](JetBrains/kotlin@v2.0.21...v2.1.0)

---
updated-dependencies:
- dependency-name: plugin.serialization
  dependency-type: direct:production
  update-type: version-update:semver-minor
- dependency-name: multiplatform
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

webinterface/build.gradle.kts

@@ -13,7 +13,7 @@ val kvisionVersion = "8.0.1"
 val webDir = file("src/jsMain/web")
 
 plugins {
-    val kotlinVersion = "2.0.21"
+    val kotlinVersion = "2.1.0"
     val kvisionVersion = "7.5.1"
 
     kotlin("plugin.serialization") version kotlinVersion