Allow using a Cross.toml beside another workspace member Cargo.toml

[Emilgardis]

Checklist

• I've looked through the issues and pull requests for similar request
• This feature could be solved with a custom docker image (optional)

Describe your request

Currently, if you have a workspace laid out like

.
Cargo.toml
Cross.toml
member/
member/Cargo.toml
member/Cross.toml

and we're currently in member, cross would not use member/Cross.toml, this should be fixed

Describe why this would be a good inclusion for cross

No response

[Emilgardis]

This is closely related to #1158 but in reverse