Don't run tutorial tests as part of nocompat test on Python3.

dulwich/tests/__init__.py

@@ -170,7 +170,8 @@ def nocompat_test_suite():
     result = unittest.TestSuite()
     result.addTests(self_test_suite())
     from dulwich.contrib import test_suite as contrib_test_suite
-    result.addTests(tutorial_test_suite())
+    if sys.version_info[0] == 2:
+        result.addTests(tutorial_test_suite())
     result.addTests(contrib_test_suite())
     return result