Fix online tests using the countries.trevorblades.com backend

[leszekhanusz]

The backend that we use for some online tests (countries.trevorblades.com) (not part of the default tests) is not affiliated to gql and is subject to changes out of our control.

Because of some of those changes, run with make all_tests were failing.

Changes:

• the websocket backend is not available anymore (See issue countries#42)
• the http endpoint is not available anymore, only the https endpoint works
• batching is not supported anymore (See issue countries#72)
• some returned error changed

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (039236c) 100.00% compared to head (0b43366) 100.00%.

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #459   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           29        29           
  Lines         2619      2619           
=========================================
  Hits          2619      2619           

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