tests: add new tests for uhashlib differences

.. these tests currently fail, but a subsequent commit will
fix them

tests/extmod/uhashlib_sha1.py

@@ -19,3 +19,10 @@ except AttributeError:
 sha1 = hashlib.sha1(b'hello')
 sha1.update(b'world')
 print(sha1.digest())
+
+sha1 = hashlib.sha1(b'hello')
+try:
+    sha1.update(u'world')
+except TypeError as e:
+    print("TypeError")
+print(sha1.digest())

tests/extmod/uhashlib_sha256.py

@@ -23,6 +23,13 @@ print(h.digest())
 
 print(hashlib.sha256(b"\xff" * 64).digest())
 
+sha256 = hashlib.sha256(b'hello')
+try:
+    sha256.update(u'world')
+except TypeError as e:
+    print("TypeError")
+print(sha256.digest())
+
 # TODO: running .digest() several times in row is not supported()
 #h = hashlib.sha256(b'123')
 #print(h.digest())