[FIR] Update testdata of FIR spec tests

compiler/tests-spec/testData/diagnostics/notLinked/coercion-to-unit/neg/1.fir.kt

@@ -1,11 +1,20 @@
+/*
+ * KOTLIN DIAGNOSTICS NOT LINKED SPEC TEST (NEGATIVE)
+ *
+ * SECTIONS: coercion-to-unit
+ * NUMBER: 1
+ * DESCRIPTION: Coercion to Unit error diagnostics absence
+ * ISSUES: KT-38490
+ */
+
 // TESTCASE NUMBER: 1
 
 val y0 = when (2) {
-    else -> if (true) {""}
+    else -> <!INVALID_IF_AS_EXPRESSION!>if<!> (true) {""}
 }
 
 val w:Any = TODO()
 
 val y1 = when (2) {
-    else -> if (true) {""} // false ok with coercion to Unit
+    else -> <!INVALID_IF_AS_EXPRESSION!>if<!> (true) {""} // false ok with coercion to Unit
 }