[FIR-TEST] Add new testdata generated after changes in previous commit

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

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