Fix for Click 8.2 breaking change

[strickvl]

Somewhere around 8.2 click introduced a breaking change around whether you could use this mix_stderr when initialising the runner, and unfortunately we now use it following the bump of Modal to modal>=1 integration dependency.

In 8.2 the internal HelpFormatter.write_dl now enforces definition-list entries to be pairs. Our CLI’s grouped help still feeds triples (category, command, summary), which now throws a TypeError, and Click exits with SystemExit(2) while printing the error. In the tests that simply run CliRunner().invoke(cli) (or run a command that shows help), that exception bubbles up as a failure.

The exit-path change hits us anywhere a test relies on CliRunner invoking the root zenml command and expects the call to succeed cleanly.

This PR updates the CLI formatting code to handle this case.