i18n(fr): update `guides/authentication.mdx`

[ArmandPhilippot]

Description (required)

Updates the French translation of guides/authentication:

• to add changes from #11899 and #11939
• to slightly reword some parts and replace double quotes with French quotes (related to the French i18n guide update)

Related issues & labels (optional)

• Suggested label: i18n

[netlify[bot]]

✅ Deploy Preview for astro-docs-2 ready!

Built without sensitive environment variables

Name	Link
🔨 Latest commit	614eb3ef75343b6eb3a3d5b3102052d9a7c0e3b2
🔍 Latest deploy log	https://app.netlify.com/projects/astro-docs-2/deploys/6862a18d6c11880008c6b5b1
😎 Deploy Preview	https://deploy-preview-11938--astro-docs-2.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify project configuration.

[astrobot-houston]

Lunaria Status Overview

🌕 This pull request will trigger status changes.

Learn more

By default, every PR changing files present in the Lunaria configuration's files property will be considered and trigger status changes accordingly.

You can change this by adding one of the keywords present in the ignoreKeywords property in your Lunaria configuration file in the PR's title (ignoring all files) or by including a tracker directive in the merged commit's description.

Tracked Files

File	Note
fr/guides/authentication.mdx	Localization changed, will be marked as complete. 🔄️

Warnings reference

Icon	Description
🔄️	The source for this localization has been updated since the creation of this pull request, make sure all changes in the source have been applied.