fix: spin build failed

[dierbei]

Fix #108

[Mossaka]

Thanks for your contribution!

This does resolve the problem that #108 brings. However, I'd love to propose an alternative way - instead of adding another target at the build-spin step, could we add it to a install-rust-targets target that does something similar to https://github.com/deislabs/containerd-wasm-shims/blob/main/.github/workflows/build.yaml#L30-L33?

This allows us to reuse the same step in both the CI and local dev environment.

[dierbei]

@microsoft-github-policy-service agree

[Mossaka]

@dierbei could you please sign your commits?

[dierbei]

@Mossaka I tried doing a rebase so maybe the commit will be clearer.