PEP 798: Small Typo Fix (#4500)

fix typo: extra copy of genexp in motivation section

Author: adqm

peps/pep-0798.rst

@@ -88,7 +88,7 @@ an additional alternative::
     [*it for it in its]  # list with the concatenation of iterables in 'its'
     {*it for it in its}  # set with the union of iterables in 'its'
     {**d for d in dicts} # dict with the combination of dicts in 'dicts'
-    (*it for it in its)  # generator of the concatenation of iterables in 'its'   (*it for it in its)
+    (*it for it in its)  # generator of the concatenation of iterables in 'its'
 
 This proposal also extends to asynchronous comprehensions and generator
 expressions, such that, for example, ``(*ait async for ait in aits())`` is