Update Kotlin to 1.5.0

Author: ilya-g

build.gradle.kts

@@ -1,15 +1,7 @@
-buildscript {
-    repositories {
-        mavenCentral()
-    }
-    dependencies {
-        classpath("org.jetbrains.kotlin:kotlin-gradle-plugin:1.4.30")
-    }
-}
-
 plugins {
     id("kotlinx.team.infra") version "0.3.0-dev-64"
-    kotlin("plugin.serialization") version "1.4.30"
+    kotlin("multiplatform") version "1.5.0" apply false
+    kotlin("plugin.serialization") version "1.5.0" apply false
 }
 
 infra {

settings.gradle

@@ -1,6 +1,7 @@
 pluginManagement {
     repositories {
         maven { url 'https://maven.pkg.jetbrains.space/kotlin/p/kotlinx/maven' }
+        mavenCentral()
         gradlePluginPortal()
     }
 }