Fix reference to exercise 5 (#311)

First, check if the array length is greater than 1, and then compare.

Author: edoardob90

tutorial/tests/test_11_functional_programming.py

@@ -248,7 +248,7 @@ def test_exercise4(
 
 
 def reference_exercise5(words: list[str]) -> list[str]:
-    return list(filter(lambda x: x == x[::-1] and len(x) > 1, words))
+    return list(filter(lambda x: len(x) > 1 and x == x[::-1], words))
 
 
 def test_exercise5(function_to_test: Callable[[list[str]], list[str]]):