add unit test 4, which AI wrote in github comments

data/test/scenarios/unit_test_4.cfg

@@ -0,0 +1,13 @@
+# This test checks that [end_turn] is working.
+
+{GENERIC_UNIT_TEST "unit_test_4" (
+    [event]
+        name = start
+        [end_turn]
+        [/end_turn]
+    [/event]
+    [event]
+        name = side 2 turn 1
+        {RETURN ([true][/true])}
+    [/event]
+)}