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

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

@@ -0,0 +1,13 @@
+// KT-7857: when exhaustiveness does not take previous nullability checks into account
+fun foo(arg: Boolean?): Int {
+    if (arg != null) {
+        return when (arg) {
+            true -> 1
+            false -> 0
+            // else or null branch should not be required here!
+        }
+    } 
+    else {
+        return -1
+    }
+}