Also run doctests in CI

Author: JanEricNitschke

src/test_typing_extensions.py

@@ -9574,6 +9574,10 @@ def test_sentinel_not_picklable(self):
         ):
             pickle.dumps(sentinel)
 
+def load_tests(loader, tests, pattern):
+    import doctest
+    tests.addTests(doctest.DocTestSuite(typing_extensions))
+    return tests
 
 if __name__ == '__main__':  # pragma: no cover
     main()