PERF: Suppress ix warnings benchmarks

[leeyspaul]

• closes PERF: benchmarks are hitting .ix & other warnings #27217
• tests added / passed
• passes black pandas
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

TODO: add tests for suppressed warnings.

[leeyspaul]

@jreback for review. Thank you!

[jorisvandenbossche]

@leeyspaul I think you are adding the filterwarnings in the wrong place. We don't want to suppress those warnings in general (that's why we put them there, so users see them), but only in the benchmarks. So it is inside the benchmarking code that we would need to add filters.

[leeyspaul]

@jorisvandenbossche Ahhh right, thank you for that. I believe I've suppressed the appropriate warnings in the right places this time around! Please take a look when able. :)

[jreback]

thanks @leeyspaul