fix(extras.copilot-chat): small ui fix for which-key in visual mode (#3573)

## What is this PR for?
- Just a small fix for which-key in visual mode that the authors forgot
to add.
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  why we should accept this pull request. -->

## Does this PR fix an existing issue?
- As copilot-chat has just been added to extras so i think this is new.
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## Checklist

- [x] I've read the
[CONTRIBUTING](https://github.com/LazyVim/LazyVim/blob/main/CONTRIBUTING.md)
guidelines.

lua/lazyvim/plugins/extras/coding/copilot-chat.lua

@@ -22,7 +22,7 @@ return {
       }
     end,
     keys = {
-      { "<leader>a", "", desc = "+ai" },
+      { "<leader>a", "", desc = "+ai", mode = { "n", "v" } },
       {
         "<leader>aa",
         function()