ambiguity in matmul

[CarloLucibello]

In GraphNeuralNetworks.jl the buildkite pipeline is reporting an ambiguity, see here
https://buildkite.com/julialang/graphneuralnetworks-dot-jl/builds/905/steps/canvas?sid=019b4804-b72e-4dc2-8aaa-568f0c690864#019b4804-b75a-455f-ab66-0b1b345056ff/L515

I can try to make the report a little bit more explicit, although I don't have access to an amd gpu so I'll have to work blindly.

[luraess]

This should be addressed by #874 and available on master and in the next release 2.2.0. Closing this for now but feel free to reopen if the issue persists.