Fixed #36636 -- Removed session-based storage reference from set_language() docs and docstring.

[DaniFornons]

This PR fixes outdated references in the documentation and docstring of django.views.i18n.set_language().
Since Django 4.0, the view no longer stores the chosen language in the session. It only uses the cookie defined by the LANGUAGE_COOKIE_NAME setting.
The docstring and docs have been updated accordingly to avoid confusion.

Thanks to Samriddha Kumar Tripathi and kid_alan_ on Discord for the report

Trac ticket number

ticket-36636

Branch description

Remove outdated references to session-based language storage in the set_language() view docstring and in the i18n documentation.

Checklist

• This PR targets the main branch.
• The commit message is written in past tense, mentions the ticket number, and ends with a period.
• I have checked the "Has patch" ticket flag in the Trac system.
• I have added or updated relevant tests.
• I have added or updated relevant docs, including release notes if applicable.
• I have attached screenshots in both light and dark modes for any UI changes.

[jacobtylerwalls]

Thanks for picking this up. 👍 Just some teeny suggested edits.

[jacobtylerwalls]

Thank you!