Use proper settings in the diagnostics section (#29791)

Kirill Bulatov and Cole Miller created 

Follow-up of https://github.com/zed-industries/zed/pull/29706

Release Notes:

- N/A

Co-authored-by: Cole Miller <cole@zed.dev>

Change summary

assets/settings/default.json | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

Detailed changes

assets/settings/default.json 🔗 

@@ -934,7 +934,7 @@
       // Shows all diagnostics when not specified.
       "max_severity": null
     },
-    "rust": {
+    "cargo": {
       // When enabled, Zed disables rust-analyzer's check on save and starts to query
       // Cargo diagnostics separately.
       "fetch_cargo_diagnostics": false