Relax MSRV version to 1.41.1 and test it in CI

[kngwyu]

Fixes #176. If this succeeds, patch release should follow.

[kngwyu]

Oops, it looks like that ndarray=0.14 is selected for rust-numpy:
https://github.com/PyO3/rust-numpy/pull/177/checks?check_run_id=2114810876

[kngwyu]

@mtreinish @davidhewitt
Sorry for this noisy notification, but do you have any idea for successfully compiling the example with ndarray 0.13.1?
Since cargo resolves ndarray=0.14, I am now manually editing the generated Cargo.lock by a Python script.
Also, -Z minimal-versions fails due to a dependency (ghost=0.1.0 requires older syn and quote, which causes a problem).

[messense]

Have you tried cargo update -p ndarray --precise 0.13.1 ?

[davidhewitt]

(Sorry, deleted other comment; it was wrong and unhelpful!)

Have you tried cargo update -p ndarray --precise 0.13.1 ?

Ah, this works, but only if Cargo.toml for simple-extension is modified to target ndarray = "0.13" and the [workspace] section is removed from the root Cargo.toml. (With the [workspace] section present cargo tries to unify the version across all examples, which doesn't work because the linalg example still requires 0.14.)

[kngwyu]

Have you tried cargo update -p ndarray --precise 0.13.1 ?

Many thanks for this. cargo update -p ndarray:0.14.0 --precise 0.13.1 worked.

but only if ...

Yeah, I resolve the problem by running the example outside the rust-numpy directory on CI.

(Deleted comment)

rust-lang/cargo#5340 suggests that it's discouraged to have such dependencies.

Yeah, I think this is bad, but I believe MSRV is a more serious problem.