i18n(fr): update errors/env-invalid-variables.mdx (#13931)

Co-authored-by: Thomas Bonnet <thomasbnt@protonmail.com>

Author: ArmandPhilippot

src/content/docs/fr/reference/errors/env-invalid-variables.mdx

@@ -1,5 +1,5 @@
 ---
-title: Variables d'environnement non valides
+title: Variables d'environnement non valides.
 i18nReady: true
 githubURL: https://github.com/withastro/astro/blob/main/packages/astro/src/core/errors/errors-data.ts
 ---