Minor. Add more tests

compiler/testData/codegen/box/inlineClasses/kt37998Generic.kt

@@ -0,0 +1,18 @@
+// WITH_STDLIB
+// WORKS_WHEN_VALUE_CLASS
+// LANGUAGE: +ValueClasses, +GenericInlineClassParameter
+
+OPTIONAL_JVM_INLINE_ANNOTATION
+value class Z<T: Int>(val x: T)
+
+class A {
+    fun foo() = Z(42)
+}
+
+fun test(a: A?) = a?.foo()!!
+
+fun box(): String {
+    val t = test(A())
+    if (t.x != 42) throw AssertionError("$t")
+    return "OK"
+}