WebSearch: fix for regression test link targets

• On one build node, four regression test cases were failing because they were expecting a link URL arguments to be written in certain order, while the code prints arguments from a dictionary without imposing any particular order.
  
  This commit fixes the tests by simply checking for link label instead of checking for link target URL, because in this particular case it is sufficient. Later, we may want to build URLs according to a certain preferred order of arguments, e.g. p before sf, etc.