CLN: GH29547 format with f-strings
replace .format() for f-strings in the following:

1. pandas/tests/series/indexing/test_numeric.py
2. pandas/tests/series/indexing/test_take.py
3. pandas/tests/series/indexing/test_where.py


Hello @DanBasson! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:





There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2020-06-20 16:23:55 UTC lgtm. ping on green (the 3.9 biuld is failing but x that) i don't understand what you are saying (i'm new...).
what is "ping on green"? > i don't understand what you are saying (i'm new...).
> what is "ping on green"?

it means when the CI are all green, comment. note that the CI is currently having various issues. @jreback 

the CI are all green.
i got some errors which i couldn't understand just to make sure (this error should be patched), can you merge upstream master and then ping on green. Turns out that was the problem.
thank you very much @jreback  thanks @DanBasson 