Check diagnostic refresh support from client capability (#15014)
## Summary
Per the LSP spec, the property name is `workspace.diagnostics` with an
`s` at the end but the `lsp-types` dependency uses
`workspace.diagnostic` (without an `s`). Our fork contains this fix
(https://github.com/astral-sh/lsp-types/commit/0f58d628799182647f688908ba752a33f854fb3a)
so we should avoid the hardcoded value.
The implication of this is that the client which doesn't support
workspace refresh capability didn't support the [dynamic
configuration](https://docs.astral.sh/ruff/editors/features/#dynamic-configuration)
feature because the server would _always_ send the workspace refresh
request but the client would ignore it. We have a fallback logic to
publish the diagnostics instead:
https://github.com/astral-sh/ruff/blob/5f6fc3988b5ce19790746921bd80cde9b646d690/crates/ruff_server/src/server/api/notifications/did_change_watched_files.rs#L28-L40
fixes: #15013
## Test Plan
### VS Code
https://github.com/user-attachments/assets/61ac8e6f-aa20-41cc-b398-998e1866b5bc
### Neovim
https://github.com/user-attachments/assets/4131e13c-3fba-411c-9bb7-478d26eb8d56
