Update a Kotlin version to second 1.9.20 RC

Author: fzhinkin

core/jvm/src/RawSink.kt

@@ -21,9 +21,6 @@
 package kotlinx.io
 
 import java.io.Flushable
-
-@AllowDifferentMembersInActual
-@OptIn(ExperimentalStdlibApi::class, ExperimentalMultiplatform::class)
 public actual interface RawSink : AutoCloseableAlias, Flushable {
     public actual fun write(source: Buffer, byteCount: Long)
 

gradle/libs.versions.toml

@@ -1,5 +1,5 @@
 [versions]
-kotlin = "1.9.20-RC"
+kotlin = "1.9.20-RC2"
 java = "8"
 dokka = "1.8.20"
 kover = "0.7.3"