Run tests on CI with cargo-nextest

[messense]

https://github.com/nextest-rs/nextest

Try it out to see if it can help speeding up CI runs.

[messense]

test marker::tests::test_acquire_gil ... FAILED

pyo3/src/marker.rs

Lines 993 to 1010 in b8dd626

	fn test_acquire_gil() {
	const GIL_NOT_HELD: c_int = 0;
	const GIL_HELD: c_int = 1;
	let state = unsafe { crate::ffi::PyGILState_Check() };
	assert_eq!(state, GIL_NOT_HELD);
	{
	let gil = Python::acquire_gil();
	let _py = gil.python();
	let state = unsafe { crate::ffi::PyGILState_Check() };
	assert_eq!(state, GIL_HELD);
	drop(gil);
	}
	let state = unsafe { crate::ffi::PyGILState_Check() };
	assert_eq!(state, GIL_NOT_HELD);
	}

This one seems problematic with cargo-nextest.

https://nexte.st/book/how-it-works.html

[birkenfeld]

Last time I checked, nextest did not support and run doctests. So you'd have to add "cargo test --doc" as a separate step?

[messense]

Last time I checked, nextest did not support and run doctests. So you'd have to add "cargo test --doc" as a separate step?

In that case I think we should wait for nextest-rs/nextest#16, otherwise the added cargo test --doc steps might just slow things down and make the CI setup more complex.