K2: add test reproducing KT-63379

compiler/testData/diagnostics/tests/funInterface/unitInContravariantPosition.kt

@@ -0,0 +1,17 @@
+// ISSUE: KT-63379
+
+class TestDummyClass<T> {
+    fun testFun(t: T) {}
+}
+
+fun more(t: TestDummyClass<in CustomRunnable>) {
+    t.testFun { Unit }
+    t.testFun(CustomRunnable { Unit })
+    t.testFun(object : CustomRunnable {
+        override fun run() {}
+    })
+}
+
+fun interface CustomRunnable {
+    fun run()
+}