PEP 654: Fixed typo: 'distunction -> distinction' (python#2089)

pep-0654.rst

@@ -154,7 +154,7 @@ The difference between them is that ``ExceptionGroup`` can only wrap
 exceptions and selects between ``ExceptionGroup`` and ``BaseExceptionGroup``
 makes the choice automatic. In the rest of the document, when we refer to
 an exception group, we mean either an ``ExceptionGroup`` or a
-``BaseExceptionGroup``. When it is necessary to make the distunction, we
+``BaseExceptionGroup``. When it is necessary to make the distinction, we
 use the class name. For brevity, we will use ``ExceptionGroup`` in code
 examples that are relevant to both.