fix(copilot): CopilotChat.nvim has moved to main (#4931)

## Description

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maintainers
  why we should accept this pull request. -->

CopilotChat.nvim has moved to main
([ref](https://github.com/CopilotC-Nvim/CopilotChat.nvim/issues/665))

## Related Issue(s)
https://github.com/CopilotC-Nvim/CopilotChat.nvim/issues/665
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  If this PR fixes any issues, please link to the issue here.
  - Fixes #<issue_number>
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## Screenshots

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![image](https://github.com/user-attachments/assets/2970e3c0-04af-49e9-974b-d535e47b9c12)

## Checklist

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

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

@@ -17,7 +17,7 @@ end
 return {
   {
     "CopilotC-Nvim/CopilotChat.nvim",
-    branch = "canary",
+    branch = "main",
     cmd = "CopilotChat",
     opts = function()
       local user = vim.env.USER or "User"