Flaky test in els_references_SUITE

[robertoaloi]

The test occasionally fails. This is most common in CI, it never seems to fail locally.

%%% els_references_SUITE ==> ignore_open_watched_file_added: FAILED
%%% els_references_SUITE ==> 
Failure/Error: ?assertEqual(2, length ( Locations ))
  expected: 2
       got: 1
      line: 710
   comment: {{expected,[#{range => #{from => {6,3},to => {6,22}},
                          uri =>
                              <<"file:///__w/erlang_ls/erlang_ls/_build/test/lib/els_lsp/priv/code_navigation/src/watched_file_c.erl">>},
                        #{range => #{from => {6,3},to => {6,22}},
                          uri =>
                              <<"file:///__w/erlang_ls/erlang_ls/_build/test/lib/els_lsp/priv/code_navigation/src/watched_file_b.erl">>}]},
             {actual,[#{range =>
                            #{'end' => #{character => 21,line => 5},
                              start => #{character => 2,line => 5}},
                        uri =>
                            <<"file:///__w/erlang_ls/erlang_ls/_build/test/lib/els_lsp/priv/code_navigation/src/watched_file_b.erl">>}]}}