i18n(fr): update tutorials/add-view-transitions.mdx

[ArmandPhilippot]

Description (required)

• Add updates made to tutorials/add-view-transitions.mdx in #8707
• Replace page "About" with page "À propos" (since the other ones are translated)
• Translate a missing Update to Astro v4.x comment
• Add a space before colon inside comments written in French
• Remove some extra indent on new lines (it was messing with syntax highlighting)

Related issues & labels (optional)

• Suggested label: i18n