Fix test on Linux

Author: vidartf

jupyter_server/services/contents/filemanager.py

@@ -70,8 +70,6 @@ def _default_preferred_dir(self):
                     DeprecationWarning,
                     stacklevel=3,
                 )
-                if not os.path.isdir(value):
-                    raise TraitError(_i18n("No such preferred dir: %r") % value)
                 if not (value + os.path.sep).startswith(self.root_dir):
                     raise TraitError("%s is outside root contents directory" % value)
                 return os.path.relpath(value, self.root_dir).replace(os.path.sep, "/")

tests/test_serverapp.py

@@ -406,4 +406,4 @@ def test_absolute_preferred_dir_not_root_subdir_set(tmp_path, jp_configurable_se
     if os.name == "nt":
         assert "is not a relative API path" in str(error)
     else:
-        assert "No such directory" in str(error)
+        assert "Preferred directory not found" in str(error)