Warn when there are deps with the same keys and different `:local/root`s

[mpereira]

Is your feature request related to a problem? Please describe.
I had a project and a base with the same dep key name, which caused only one of them to be in the merged development deps.

Describe the solution you'd like
It's a small nice-to-have, but poly could warn when this situation happens.

[tengstrand]

Did you specify both the base and the project in your development ./deps file? @mpereira