python.pkgs.sqlalchemy: use pytest_30 and don't use pytest_xdist

pkgs/development/python-modules/sqlalchemy/default.nix

@@ -1,7 +1,7 @@
 { lib
 , fetchPypi
 , buildPythonPackage
-, pytest
+, pytest_30
 , mock
 , pytest_xdist
 , isPy3k
@@ -18,12 +18,12 @@ buildPythonPackage rec {
     sha256 = "2a98ac87b30eaa2bee1f1044848b9590e476e7f93d033c6542e60b993a5cf898";
   };
 
-  checkInputs = [ pytest mock pytest_xdist ]
-    ++ lib.optional (!isPy3k) pysqlite;
-
-  # Test-only dependency pysqlite doesn't build on Python 3. This isn't an
-  # acceptable reason to make all dependents unavailable on Python 3 as well
-  #doCheck = !(isPyPy || isPy3k);
+  checkInputs = [
+    pytest_30
+    mock
+#     Disable pytest_xdist tests for now, because our version seems to be too new.
+#     pytest_xdist
+  ] ++ lib.optional (!isPy3k) pysqlite;
 
   checkPhase = ''
     py.test