fix python plugin example (#7599)

# Description

_(Thank you for improving Nushell. Please, check our [contributing
guide](../CONTRIBUTING.md) and talk to the core team before making major
changes.)_

_(Description of your pull request goes here. **Provide examples and/or
screenshots** if your changes affect the user experience.)_

# User-Facing Changes

_(List of all changes that impact the user experience here. This helps
us keep track of breaking changes.)_

# Tests + Formatting

Don't forget to add tests that cover your changes.

Make sure you've run and fixed any issues with these commands:

- `cargo fmt --all -- --check` to check standard code formatting (`cargo
fmt --all` applies these changes)
- `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used -A
clippy::needless_collect` to check that you're using the standard code
style
- `cargo test --workspace` to check that all tests pass

# After Submitting

If your PR had any user-facing changes, update [the
documentation](https://github.com/nushell/nushell.github.io) after the
PR is merged, if necessary. This will help us keep the docs up to date.

crates/nu_plugin_python/nu_plugin_python_example.py

@@ -103,6 +103,7 @@ def signatures():
                 "search_terms": ["Python", "Example"],
                 "is_filter": False,
                 "creates_scope": False,
+                "allows_unknown_args": False,
                 "category": "Experimental",
             }
         ]