[FIR] Don't ignore annotations on when subjects

^KT-53565 Fixed

compiler/testData/diagnostics/tests/missingWrongAnnotationTarget.kt

@@ -0,0 +1,12 @@
+// FIR_IDENTICAL
+// ISSUE: KT-53565
+
+@Target(AnnotationTarget.CLASS)
+annotation class InvalidAnn
+
+fun wrongAnnotationTargetInWhenSubject() {
+    // Error expected on annotation
+    when(<!WRONG_ANNOTATION_TARGET!>@InvalidAnn<!> val x = 0) {
+        0 -> {}
+    }
+}