[nomerge] SI-6667 Demote a new ambiguity error to a lint warning.

In the interests of not breaking source compability.
A few projects are relying on this bug.

Should not be merged to master.
Merge pull request #2063 from retronym/ticket/6667-2.10.x-revert

[nomerge] SI-6667 Demote a new ambiguity error to a lint warning.