Fix for Zygote 0.6.30 breaking our tests (#409)

* restrict Zygote to <0.6.30

* revert Zygote test restriction and add finer-grained testset

* Update test/utils.jl

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

* revert testset

* mark test_broken

* Use `@test_throws` instead of `@test_broken`

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: David Widmann <devmotion@users.noreply.github.com>

Author: 3 people

test/test_utils.jl

@@ -100,7 +100,7 @@ function check_zygote_type_stability(f, args...; ctx=Zygote.Context())
     @inferred f(args...)
     @inferred Zygote._pullback(ctx, f, args...)
     out, pb = Zygote._pullback(ctx, f, args...)
-    @inferred pb(out)
+    @test_throws ErrorException @inferred pb(out)
 end
 
 function test_ADs(