python39Packages.pytest-testmon: fix build

The tests have been removed upstream in late january:
decb4f4fde

which means this package has been broken since 1.3.0 on March 2nd

pkgs/development/python-modules/pytest-testmon/default.nix

@@ -16,16 +16,11 @@ buildPythonPackage rec {
     sha256 = "sha256-6gWWCtm/GHknhjLyRdVf42koeaSKzk5/V0173DELmj0=";
   };
 
-  propagatedBuildInputs = [ coverage ];
+  propagatedBuildInputs = [ pytest coverage ];
 
-  checkInputs = [ pytest ];
-
-  # avoid tests which try to import unittest_mixins
-  # unittest_mixins doesn't seem to be very active
-  checkPhase = ''
-    cd test
-    pytest test_{core,process_code,pytest_assumptions}.py
-  '';
+  # The project does not include tests since version 1.3.0
+  doCheck = false;
+  pythonImportsCheck = [ "testmon" ];
 
   meta = with lib; {
     homepage = "https://github.com/tarpas/pytest-testmon/";