DOC: Fix typo in to_html and to_string docs
**UPDATE:** This started as an upgrade of Python in environment.yml, now it's just about fixing an issue with a period is duplicated in both the template and the variables.


I guess the only reason we require Python 3.10 for the development environments and run the docs is because it wasn't updated for a long time. Not sure if it'd be better to unpin, which I assume would get us the latest version of Python. Happy to do that here too.
+1 to unpin Python here Just FYI, I think there are some configurations like pre-commit/mypy/etc. that have a "Python version" configuration that may be useful to (un)sync since they are dependent on the Python version installed by `environment.yml` I'll leave this PR just for the typo in the docs (which doesn't seem was the cause for the doc build to fail). This is a bit more time consuming than I initially thought, and I prefer to focus on other things now. I created #61585 for this, probably someone from the community will take care of it, as it's a great first time issue. /preview Website preview of this PR available at: https://pandas.pydata.org/preview/pandas-dev/pandas/61555/