Add test in syntax_comprehension.py

Author: yt2b

extra_tests/snippets/syntax_comprehension.py

@@ -41,3 +41,8 @@
 assert 'c' not in locals()
 assert 'b' not in globals()
 assert 'c' not in globals()
+
+
+def f():
+    # Test no panic occured.
+    [[x := 1 for j in range(5)] for i in range(5)]