completion snippets behave badly in the presence of combining diacritics

### Your environment

Which LSP client (editor/plugin) do you use?
Neovim, astrovim (which I think is using luasnips and nvim-cmp)

The actual crash is in nvim-cmp, so it's quite possibly a bug there, but at least turning off `plugin.ghcide-completions.config.snippetsOn` seems to fix things, so opening this issue just in case anyone else searches combining diacritics snippets or something.

Sorry for the low quality report!

Which version of HLS do you use and how did you install it?
`haskell-language-server version: 2.9.0.0 (GHC: 9.8.2)`

### Steps to reproduce

- Set up astrovim and enable the haskell community pack (definitely a smaller repro)
- Open a haskell file
- wait for hls to init
- type `â` (a with a combining circumflex)
- observe something like:

```
Error executing vim.schedule lua callback: ...l/share/astrovim/lazy/nvim-cmp/lua/cmp/utils/snippet.lua:409: snippet parsing failed.
stack traceback:
[C]: in function 'error'
...l/share/astrovim/lazy/nvim-cmp/lua/cmp/utils/snippet.lua:409: in function 'parse'
.../e/.local/share/astrovim/lazy/nvim-cmp/lua/cmp/entry.lua:130: in function 'callback'
...cal/share/astrovim/lazy/nvim-cmp/lua/cmp/utils/cache.lua:38: in function 'get_word'
.../e/.local/share/astrovim/lazy/nvim-cmp/lua/cmp/entry.lua:81: in function 'callback'
...cal/share/astrovim/lazy/nvim-cmp/lua/cmp/utils/cache.lua:38: in function 'get_offset'
...e/.local/share/astrovim/lazy/nvim-cmp/lua/cmp/source.lua:353: in function ''
vim/_editor.lua: in function
````