floor with degrees (NoUnits) and digits fails due to method ambiguity

[JeffFessler]

MWE:

using Unitful: mm, °

x = 3.001mm
floor(typeof(x), x, digits=2) # works

a = 3.001°
floor(typeof(a), a, digits=2) # fails due to method ambiguity

Presumably because degrees are the NoUnits flavor.
This one is pretty opaque to me so I'm not sure where to begin for PR.

Perhaps related to #326?
In fact I suspect that if #328 were merged then I probably would just use floor(a, digits=2) for my use case (matching how non-unit values work), so it would be great to bump that one!