Markup Extension doc: Default English translation has been replaced with Russian

[webprofusion-chrisc]

As per https://github.com/AvaloniaUI/avalonia-docs/commit/b42036516bb8ca9a84336a7f78668e179a5ad9c6

Currently both the sidebar and doc page for https://docs.avaloniaui.net/docs/reference/mark-up-extensions are in Russian on the main site.

[maxkatz6]

Thank you for reporting! Fixed.