Tweak tests to match wrt. natural tangents

Author: ToucheSir

test/projection.jl

@@ -212,7 +212,7 @@ struct NoSuperType end
         @test ProjectTo(I)(123) === NoTangent()
         @test ProjectTo(2 * I)(I * 3im) === 0.0 * I
         @test ProjectTo((4 + 5im) * I)(Tangent{typeof(im * I)}(; λ = 6)) === (6.0 + 0.0im) * I
-        @test ProjectTo(7 * I)(Tangent{typeof(2I)}()) == ZeroTangent()
+        @test ProjectTo(7 * I)(Tangent{typeof(2I)}()) == 0.0I
     end
 
     @testset "LinearAlgebra: $adj vectors" for adj in [transpose, adjoint]
@@ -413,7 +413,6 @@ struct NoSuperType end
         @test pb(ZeroTangent()) isa AbstractZero  # was a method ambiguity!
 
         # all projectors preserve Zero, and specific type, via one fallback method:
-        @test ProjectTo(pi)(ZeroTangent()) === ZeroTangent()
         @test ProjectTo(pi)(NoTangent()) === NoTangent()
         pv = ProjectTo(sprand(30, 0.3))
         @test pv(ZeroTangent()) === ZeroTangent()

test/rules.jl

@@ -94,7 +94,7 @@ _second(t) = Base.tuple_type_head(Base.tuple_type_tail(t))
     frx, nice_pushforward = frule((dself, 1), nice, 1)
     @test nice_pushforward === ZeroTangent()
     rrx, nice_pullback = rrule(nice, 1)
-    @test (NoTangent(), ZeroTangent()) === nice_pullback(1)
+    @test (NoTangent(), 0.0) === nice_pullback(1)
 
     # Test that these run. Do not care about numerical correctness.
     @test frule((nothing, 1.0, 1.0, 1.0), varargs_function, 0.5, 0.5, 0.5) == (1.5, 3.0)