Fix WASM CI for Rust 1.84 release

[alamb]

Which issue does this PR close?

Closes #.

Rationale for this change

Rust 1.84 was released yesterday: https://blog.rust-lang.org/2025/01/09/Rust-1.84.0.html 🎉

Unfortunately, this broke our WASM builds:

https://github.com/apache/arrow-rs/actions/runs/12698871454/job/35398265255

Installing stable
info: syncing channel updates for 'stable-x86_64-unknown-linux-gnu'
info: latest update on 2025-01-09, rust version 1.84.0 (9fc6b4312 2025-01-07)
error: component 'rust-std' for target 'wasm32-wasi' is unavailable for download for channel 'stable'
If you don't need the component, you could try a minimal installation with:

    rustup toolchain add stable --profile minimal

If you require these components, please install and use the latest successful build version,
which you can find at <https://rust-lang.github.io/rustup-components-history>.

After determining the correct date, install it with a command such as:

    rustup toolchain install nightly-2018-12-27

Then you can use the toolchain with commands such as:

    cargo +nightly-2018-12-27 build

What changes are included in this PR?

1. Update the name of the wasm target to reflect the new name. See this blog for details: https://blog.rust-lang.org/2024/04/09/updates-to-rusts-wasi-targets.html

Are there any user-facing changes?

No, this is only a CI change

[alamb]

Thank you for the review @tustvold

[alamb]

Merging this one in to get CI passig