chore(types): fix wrong type

[rchl]

Those type errors don't show up normally because this package doesn't use good stubs for mdpopups but it does show up when using LSP stubs.

/usr/local/workspace/lsp/lsp_maintainers/repositories/LSP-copilot/plugin/ui/chat.py
  /usr/local/workspace/lsp/lsp_maintainers/repositories/LSP-copilot/plugin/ui/chat.py:185:42 - error: Argument of type "Sheet" cannot be assigned to parameter "sheet" of type "HtmlSheet" in function "update_html_sheet"
    "Sheet" is not assignable to "HtmlSheet" (reportArgumentType)
/usr/local/workspace/lsp/lsp_maintainers/repositories/LSP-copilot/plugin/ui/completion.py
  /usr/local/workspace/lsp/lsp_maintainers/repositories/LSP-copilot/plugin/ui/completion.py:242:13 - warning: No parameter named "layout" (reportCallIssue)

[rchl]

This is a problem when testing in LSP repo - https://github.com/sublimelsp/LSP/actions/runs/28530627354/job/84578855392

The types of ST layout are:

• custom Layout in LSP-copilot stubs
• dict[str, Any] in LSP stubs
• dict[str, Value] in ST's own types

So it's all a mess that's why I'm just ignoring those issues.

[jfcherng]

Thanks!