[T5, examples] replace heavy t5 models with tiny random models (#3556)

* replace heavy t5 models with tiny random models as was done by sshleifer

* fix isort

examples/translation/t5/test_t5_examples.py

@@ -37,7 +37,7 @@ class TestT5Examples(unittest.TestCase):
 
         testargs = [
             "evaluate_wmt.py",
-            "t5-small",
+            "patrickvonplaten/t5-tiny-random",
             str(tmp_source),
             str(output_file_name),
             str(tmp_target),