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

compiler/testData/diagnostics/tests/when/NoElseExpectedUnit.fir.kt

@@ -0,0 +1,7 @@
+fun foo(x: Int) {
+    val y: Unit = when (x) {
+        2 -> {}
+        3 -> {}
+    }
+    return y
+}