i18n(fr): add other small changes from 6.4 to guides & references

[ArmandPhilippot]

Description (required)

Adds the remaining small changes from #13945 to the French translations of migrate-to-astro/index.mdx, content-loader-reference.mdx, modules/astro-content.mdx, and programmatic-reference.mdx.

In programmatic-reference.mdx, I only updated the l193 not the whole file. 😅 But, it seems the file was using CRLF instead of LF as the other files... and so the change is wanted.
I see the same diff in #13461 (well, the opposite actually). It seems this was introduced by 7cec69e I don't know what happened (a misclick or wrong shortcut before committing!?)

Related issues & labels (optional)

• Suggested label: i18n

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Tracked Files

File	Note
fr/guides/migrate-to-astro/index.mdx	Localization changed, will be marked as complete.
fr/reference/content-loader-reference.mdx	Localization changed, will be marked as complete.
fr/reference/modules/astro-content.mdx	Localization changed, will be marked as complete.
fr/reference/programmatic-reference.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.

[thomasbnt]

LGTM