Fix config change notification using remote neovim

[mopp]

What kind of change does this PR introduce?

• Fix

Did this PR introduce a breaking change?

A breaking change includes anything that breaks backwards compatibility either at compile or run time.

• No

Background

I got the error below connecting remote neovim on my machine.

Error detected while processing function NeovideNotifycursor_animation_lengthChanged:
line     1:
E475: Invalid argument: Channel doesn't exist.

g:neovide_channel_id has 3 in my environment.
But the embedded Vim script always uses 1.

What I did

This PR just makes it use g:neovide_channel_id.
I don't know how to write the tests.
Please tell me where I should put the tests or merge the PR and add tests in another PR 🙏

How to reproduce

macOS Monterey 12.6.7

> /opt/homebrew/bin/nvim --version
NVIM v0.9.2
Build type: Release
LuaJIT 2.1.0-beta3

   system vimrc file: "$VIM/sysinit.vim"
  fall-back for $VIM: "/opt/homebrew/Cellar/neovim/0.9.2/share/nvim"

Run :checkhealth for more info

> /opt/homebrew/bin/nvim --headless --listen localhost:6666 -u NONE

> neovide --version
neovide 0.11.2

> neovide --server=localhost:6666

Change a neovide config via command line mode on neovide started above.

let g:neovide_scroll_animation_length = 0.3

Then, neovide causes the error.

[mopp]

I faced the same error when I quit neovide by :q.

[fredizzimo]

This will also be partially fixed by #2062, but that one does not deal with the changed listeners, even if it probably should.

So, let's merge this one first.

[fredizzimo]

@mopp,

The formatting is slightly wrong, but you can run cargo fmt to fix it.

[mopp]

@fredizzimo Thanks! I did cargo fmt 👍

[fredizzimo]

Thank you!