test/dates: assume NoUnits instead of MethodErrors in the case of Date types with ambiguous units

For example, Years are not always the same length, so they do not have
unambiguous units. Many abstract Date types also do not have units.

Author: SeSodesa

test/dates.jl

@@ -12,14 +12,14 @@
             @test_throws MethodError dimension(T(1))
             @test_throws MethodError Unitful.numtype(T)
             @test_throws MethodError Unitful.numtype(T(1))
-            @test_throws MethodError unit(T)
-            @test_throws MethodError unit(T(1))
+            @test unit(T) == NoUnits
+            @test unit(T(1)) == NoUnits
         end
 
         for p = (CompoundPeriod, CompoundPeriod(), CompoundPeriod(Day(1)), CompoundPeriod(Day(1), Hour(-1)))
             @test dimension(p) === 𝐓
             @test_throws MethodError Unitful.numtype(p)
-            @test_throws MethodError unit(p)
+            @test unit(p) == NoUnits
         end
     end