Python: Allow except* to be written as except *

Turns out, `except*` is actually not a token on its own according to the
Python grammar. This means it's legal to write `except *foo: ...`, which
we previously would consider a syntax error.

To fix it, we simply break up the `except*` into two separate tokens.

python/extractor/tests/parser/exception_groups_new.py

@@ -19,3 +19,8 @@ else:
 finally:
     u
     v
+
+try:
+    pass
+except *foo as e:
+    pass