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/tsg-python/tsp/grammar.js

@@ -309,7 +309,8 @@ module.exports = grammar({
     ),
 
     except_group_clause: $ => seq(
-      'except*',
+      'except',
+      '*',
       seq(
         field('type', $.expression),
         optional(seq(