update expected output

ruby/ql/test/library-tests/dataflow/string-flow/string-flow.expected

@@ -12,6 +12,7 @@ edges
 | string_flow.rb:10:29:10:29 | b :  | string_flow.rb:10:10:10:30 | call to try_convert |
 | string_flow.rb:14:9:14:18 | call to source :  | string_flow.rb:15:10:15:17 | ... % ... |
 | string_flow.rb:14:9:14:18 | call to source :  | string_flow.rb:15:17:15:17 | a :  |
+| string_flow.rb:14:9:14:18 | call to source :  | string_flow.rb:16:10:16:29 | ... % ... |
 | string_flow.rb:14:9:14:18 | call to source :  | string_flow.rb:16:28:16:28 | a :  |
 | string_flow.rb:14:9:14:18 | call to source :  | string_flow.rb:17:10:17:10 | a :  |
 | string_flow.rb:14:9:14:18 | call to source :  | string_flow.rb:17:10:17:18 | ... % ... |