Cargo test with minimal versions fails

[Nemo157]

proptest depends on rand, which currently fails to build with minimal versions: rust-random/rand#741

Once that's resolved should try to change the minimal CI job from just building to actually running the tests.

[chrysn]

Can't we just increment the MSRV? The issue is 4 years old, I doubt anyone is still on that stable version.

[Nemo157]

This isn't about MSRV, that policy isn't actually stated but my standard policy is to only guarantee support of the latest stable at time of a release. It's about using cargo update -Z minimal-versions and running the tests with that, to check that the dependency declarations are correct (it doesn't guarantee that it'll work with all valid dependency combinations, but testing the minimum and maximum boundaries go a long way towards it).

There's a job doing cargo minimal-versions check already, and running cargo minimal-versions test locally it looks like it is actually working now (the version of rand being chosen must be high enough to work). I just need to figure out some nice way to have an optional job to run the test now (I share my github-actions configuration between multiple repos and some others don't work still).