Fix Cargo.toml formatting (#7886)

This PR disables the formatting for `.toml` files within the Zed repo,
as the formatter provided by the TOML language server messes things up.

Release Notes:

- N/A

.zed/settings.json

@@ -1,6 +1,9 @@
 {
-  "JSON": {
-    "tab_size": 4
+  "languages": {
+    "TOML": {
+      "formatter": "prettier",
+      "format_on_save": "off"
+    }
   },
   "formatter": "auto"
 }