bpo-38100: Fix spelling error in unittest.mock code (GH-16168)

(cherry picked from commit a9187c3)

Co-authored-by: marcoramirezmx <55331462+marcoramirezmx@users.noreply.github.com>

Lib/unittest/mock.py

@@ -1974,9 +1974,9 @@ def _set_return_value(mock, method, name):
         method.return_value = fixed
         return
 
-    return_calulator = _calculate_return_value.get(name)
-    if return_calulator is not None:
-        return_value = return_calulator(mock)
+    return_calculator = _calculate_return_value.get(name)
+    if return_calculator is not None:
+        return_value = return_calculator(mock)
         method.return_value = return_value
         return