libstdc++: Fix up pr118196.cc test [PR118196]

The test used #include "<generator>", so FAILed everywhere with
fatal error: <generator>: No such file or directory

2024-12-28  Jakub Jelinek  <jakub@redhat.com>

	PR libstdc++/118196
	* testsuite/24_iterators/range_generators/pr118196.cc: Include
	<generator> rather than "<generator>".