Match progress token's prefix to detect disk-based diagnostic progress

The new version of rust-analyzer changed the disk-based diagnostic token
to `rust-analyzer/checkOnSave/0`. The trailing number could be different
from 0 when there are multiple Rust projects open using the same rust-analyzer
instance.

As such, with this commit we will perform a prefix match as opposed to a strict
equality check when detecting a disk-based diagnostics progress token.

crates/zed/src/languages/rust.rs

@@ -93,7 +93,7 @@ impl LspAdapter for RustLspAdapter {
     }
 
     async fn disk_based_diagnostics_progress_token(&self) -> Option<String> {
-        Some("rustAnalyzer/cargo check".into())
+        Some("rust-analyzer/checkOnSave".into())
     }
 
     async fn process_diagnostics(&self, params: &mut lsp::PublishDiagnosticsParams) {