Accept diff is not working on `gitcommit` anymore

[jiz4oh]

Hi, thank you create the powerful plugin.

I upgraded the plugin recently and I found the <c-y> is broken on the gitcommit.

My workflow is described below:

1. open fugitive
2. call :Git commit to open the gitcommit window
3. call CopilotChatCommit
4. call <c-y> to put the commit messages to the gitcommit window

The workflow works fine until I upgrade the plugin.

I try to debug the why and I found the copilot.chat:get_closest_block() return

{
  content = "fix(yarepl): correct aider source syntax property\n\nChanges the configuration property from 'source_func' to 'source_syntax' to \nmatch the expected configuration parameter name in yarepl plugin.",
  end_line = 15,
  header = {
    filename = "code-block",
    filetype = "gitcommit"
  },
  start_line = 12
}

and get_diff return nil.

hope the info can help you