Regression: panic messages about invalid mdtests are now swallowed by mdtest

[AlexWaygood]

Following #15241, some of the internal error messages from red_knot_test are now swallowed by the framework, for example this one here:

ruff/crates/red_knot_test/src/lib.rs

Lines 32 to 37 in b264489

	let suite = match test_parser::parse(short_title, &source) {
	Ok(suite) => suite,
	Err(err) => {
	panic!("Error parsing `{path}`: {err:?}")
	}
	};

On a PR branch I was working on, I got this (not very informative!) test failure:

If I revert 75015b0 on that PR branch, I get this instead, which is much more helpful:

[dcreager]

The panic that is being swallowed is not within the closure that is wrapped in catch_unwind. I think the issue here is that the panic hook is global, and so if you're running tests concurrently, one thread might install the custom panic hook for its catch_unwind call while another thread is in the middle of e.g. this parse operation that might fail.