Python runner: fix help message (#30259)

Well, the first part of the help message. I still have NO idea
how to get the test parameters from the individual tests exposed.

scripts/tests/yaml/runner.py

@@ -144,7 +144,7 @@ class ParserGroup:
 class YamlTestParserGroup(click.Group):
     def format_options(self, ctx, formatter):
         """Writes all the options into the formatter if they exist."""
-        if ctx.custom_options:
+        if getattr(ctx, 'custom_options', None):
             params_copy = self.params
             non_custom_params = list(filter(lambda x: x.name not in ctx.custom_options, self.params))
             custom_params = list(filter(lambda x: x.name in ctx.custom_options, self.params))