Fix tests leading to build failure on a 3.21 builder.

```
FAILED tests/m3u/test_translator.py::test_path_to_uri[test.mp3-file-file:///test.mp3]
FAILED tests/test_commands.py::CommandParsingTest::test_missing_positionals
FAILED tests/test_commands.py::CommandParsingTest::test_missing_positionals_subcommand
```