Docs formatting df join validate
- [x] closes **https://github.com/noatamir/pyladies-hh23-sprint/issues/9** (however this issue is no longer available, this was a follow-up task for the bold first list item.
- [ ] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [x] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [ ] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [ ] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

@noatamir @phofl PyLadies Hamburg Sprint

Very small updates for changing the formatting of these docs.

BEFORE:

![Screenshot 2023-07-30 at 15 35 38](https://github.com/pandas-dev/pandas/assets/23617373/f3134ecb-515b-4b52-8067-45eae236386d)

Remove the `.` between sort it and lexicographically on third list item.

AFTER:

<img width="663" alt="Screenshot 2023-07-30 at 15 35 15" src="https://github.com/pandas-dev/pandas/assets/23617373/25c69cac-4841-423f-8c10-019647f4f606">


BEFORE:
![Screenshot 2023-07-30 at 15 35 28](https://github.com/pandas-dev/pandas/assets/23617373/a810bcca-56e5-4e53-a63b-18bb88ac5a48)

Make the first list item not bold.

AFTER: 

<img width="679" alt="Screenshot 2023-07-30 at 15 35 21" src="https://github.com/pandas-dev/pandas/assets/23617373/c0e1e850-806f-4677-adb8-279b3a66d755">


Seems this failing test is failing also on the main branch. /preview No preview found for PR #54311. Did the docs build complete? Thanks @sleepypioneer 