Remove borsh from msrv builder

[bluss]

Is not supported at msrv anyway (msrv applies to defaults)

[tbu-]

LGTM.

As the compilation output shows, we'd probably have to commit a Cargo.lock to make sure that the crate continues to compile on the MSRV.

[bluss]

I see, so serde still fails too.

I think I like specific cargo upgrade --precise calls - for the msrv builder -- instead of using a lockfile?

[tbu-]

I think I like specific cargo upgrade --precise calls - for the msrv builder -- instead of using a lockfile?

That works, it doesn't pin dependencies of dependencies though. What do we want to test? Using a lockfile has the advantage of pinning everything, we see when arrayvec breaks something.

The Cargo FAQ explicitly mentions this use case for a Cargo.lock, from https://doc.rust-lang.org/cargo/faq.html#why-have-cargolock-in-version-control:

Having this snapshot of dependencies can also help when projects need to be verified against consistent versions of dependencies, like when

• Verifying a minimum-supported Rust version (MSRV) that is less than the latest version of a dependency supports

[bluss]

Sounds good, if you want to. I merged here since it was at least a step in the right direction