docs: Fix missing } in multiple formatters example (#22964)

Add a missing } in the multiple formatters example in the configuring
Zed section of the manual.

Release Notes:

- Fixed a missing } in the multiple formatters doc example

docs/src/configuring-zed.md

@@ -996,11 +996,13 @@ WARNING: `{buffer_path}` should not be used to direct your formatter to read fro
 ```json
 {
   "formatter": [
-    {"language_server": {"name": "rust-analyzer"}},
-    {"external": {
+    { "language_server": { "name": "rust-analyzer" } },
+    {
+      "external": {
         "command": "sed",
         "arguments": ["-e", "s/ *$//"]
       }
+    }
   ]
 }
 ```