Add all CARGO_RESOLVER_INCOMPATIBLE_RUST_VERSIONS to test matrix

[leon-xd]

          I guess we don't technically verify with latest Dependencies in a job rn since we do - - locked. This can be punted to a separate task:

We should have:

• jobs that run with --locked
• jobs that run with CARGO_RESOLVER_INCOMPATIBLE_RUST_VERSIONS=allow w/o --locked: this checks latest dependencies work will work in workspaces that don't use the msrv-aware resolver
• jobs that run with CARGO_RESOLVER_INCOMPATIBLE_RUST_VERSIONS=fallback w/o `--locked: this checks latest dependencies work will work in workspaces that use the msrv-aware resolver
• jobs that specifically test on MSRV

Originally posted by @wmmc88 in #314 (comment)