BENCH: Increase sample of CategoricalIndexIndexing.time_get_indexer_list benchmark
- [ ] closes #xxxx
- [ ] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

xref https://github.com/pandas-dev/pandas/pull/38476#discussion_r543329205