Add errata-ai.vale-server to deprecated extensions

[ChrisChinchilla]

• I have read the note above about PRs contributing or fixing extensions
• I have tried reaching out to the extension maintainers about publishing this extension to Open VSX (if not, please create an issue in the extension's repo using this template).
• This extension has an OSI-approved OSS license (we don't accept proprietary extensions in this repository)

Description

This extension was long deprecated in favour of https://open-vsx.org/vscode/item?itemName=chrischinchilla.vale-vscode

And I keep getting issue reports about it :)