fix: Don't detect Redwood App as multiple workspaces

[Skn0tt]

Summary

@thedavidprice reported an issue with how Netlify detects Redwood apps. Since a Redwood app is implemented as a Yarn Workspace, we detect it as being multiple apps api and web - while in reality, it should be one app.

This PR fixes our detection mechanism, by implementing an edge case for Redwood apps. We do this by matching on the redwood.toml file.

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