docs: Ruby debug configuration should be an array (#32991)

Closes #ISSUE

Small correction for something I noticed while setting up the debugger
today.

Release Notes:

- N/A

docs/src/debugger.md

@@ -383,7 +383,7 @@ To run a ruby task in the debugger, you will need to configure it in the `.zed/d
 The configuration should look like this:
 
 ```json
-{
+[
   {
     "adapter": "Ruby",
     "label": "Run CLI",
@@ -396,7 +396,7 @@ The configuration should look like this:
     // "env": {}
     // "cwd": ""
   }
-}
+]
 ```
 
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