Bugfix/add char to platformstable types (#3536)

* fixed a bug where chars were detected as unstable

* fixed test bug not picked up during build first time round

---------

Co-authored-by: Sam <sam@sksamuel.com>

kotest-common/src/commonMain/kotlin/io/kotest/mpp/stable.kt

@@ -53,4 +53,5 @@ private val allPlatformStableTypes = setOf(
    Boolean::class,
    Pair::class,
    Triple::class,
+   Char::class,
 )

kotest-common/src/jvmTest/kotlin/io/kotest/mpp/StableTest.kt

@@ -0,0 +1,32 @@
+package io.kotest.mpp
+
+import io.kotest.core.spec.style.StringSpec
+import io.kotest.matchers.shouldBe
+
+class StableTest : StringSpec({
+   "class should be correctly identified as stable" {
+      data class StableClass(
+         val string: String,
+         val int: Int,
+         val long: Long,
+         val double: Double,
+         val float: Float,
+         val byte: Byte,
+         val short: Short,
+         val boolean: Boolean,
+         val pair: Pair<String, String>,
+         val triple: Triple<String, String, String>,
+         val char: Char,
+      )
+
+      class Unstable() {
+         // something unstable here
+      }
+
+      data class UnstableDataClass(val string: String, val unstable: Unstable)
+
+      isStable(StableClass::class) shouldBe true
+      isStable(Unstable::class) shouldBe false
+      isStable(UnstableDataClass::class) shouldBe false
+   }
+})