Avoid array quoting on error states in async_process_results

The way items were quoted on error states could result in zsh
interpreting the content within double-quotes as multiple arguments to
the callback function, breaking the 6-argument promise for certain
outputs.

async.zsh

@@ -248,7 +248,7 @@ async_process_results() {
 			else
 				# In case of corrupt data, invoke callback with *async* as job
 				# name, non-zero exit status and an error message on stderr.
-				$callback "async" 1 "" 0 "$0:$LINENO: error: bad format, got ${#items} items (${(@q)items})" $has_next
+				$callback "async" 1 "" 0 "$0:$LINENO: error: bad format, got ${#items} items (${(q)items})" $has_next
 			fi
 
 			(( num_processed++ ))