'val' in 'when' subject can't have modifiers (annotations are ok)

compiler/testData/diagnostics/tests/when/withSubjectVariable/softModifierName.kt

@@ -0,0 +1,7 @@
+// !LANGUAGE: +VariableDeclarationInWhenSubject
+
+fun test(data: String) =
+    when (data.length) {
+        0 -> -1
+        else -> 42
+    }