Update AssetService:SearchAudio method with correct error "got" type (#819)

## Changes

Currently, the doocumentation for the `AssetService:SearchAudio` method
incorrectly states that the error for when `SearchKeyword` is moderated
is "Unexpected type for data, expected array got void"; instead this
error actually states that the got type is "null" (IE: "Unexpected type
for data, expected array got null"). This can be verified by running
relevant code in Studio.

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Author: AbcreatorDev

content/en-us/reference/engine/classes/AssetService.yaml

@@ -461,7 +461,7 @@ methods:
             <td><code>Class.AssetService:SearchAudio()</code> has been called too many times.</td>
           </tr>
           <tr>
-            <td>Unexpected type for data, expected array got void</td>
+            <td>Unexpected type for data, expected array got null</td>
             <td>The keyword argument was filtered.</td>
           </tr>
         </tbody>