python3Packages.astropy-extension-helpers: disable racy test

https://github.com/astropy/extension-helpers/issues/43

pkgs/development/python-modules/astropy-extension-helpers/default.nix

···
     "extension_helpers"
   ];
 
+  disabledTests = [
+    # https://github.com/astropy/extension-helpers/issues/43
+    "test_write_if_different"
+  ];
+
   pythonImportsCheck = [
     "extension_helpers"
   ];