[ci] Run cargo-semver-checks on the `wasm32-unknown-unknown` target

For wasm32-unknown-unknown, see https://github.com/obi1kenobi/cargo-semver-checks-action/issues/98

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Old text (for wasm32-wasi):

In an early draft of #1523, we ran on all targets, and the wasm32-wasi target failed ([GitHub Actions log](https://github.com/google/zerocopy/actions/runs/9944220377/job/27469879712)). For that reason, we currently skip running cargo-semver-checks on wasm32-wasi.