replace twitter->X
sphinx theme prefers using "icon_links" instead of custom keywords

https://github.com/pydata/pydata-sphinx-theme/blob/main/docs/conf.py#L165
Thanks @partev  the icon doesn't seem to be displaying correctly:
![image](https://github.com/user-attachments/assets/978b6e5c-ba7e-4401-a556-a15a4e6c585e)
even though it is referring to the correct icon name: https://fontawesome.com/icons/square-x-twitter

@mroeschke the problem is that twitter-x icon was added in fontawesome 6.4.2 https://fontawesome.com/changelog, while pandas website uses 6.1.2

how can we upgrade fontawesome?