Try to download wasi-sdk ahead of time (#42377)

This hopefully resolves the lingering test failures on linux,
but also adds some logging just in case this isn't the problem...

Release Notes:

- N/A

---------

Co-authored-by: Ben Kunkle <ben@zed.dev>

.github/workflows/run_unit_evals.yml

@@ -33,6 +33,9 @@ jobs:
     - name: steps::install_mold
       run: ./script/install-mold
       shell: bash -euxo pipefail {0}
+    - name: steps::download_wasi_sdk
+      run: ./script/download-wasi-sdk
+      shell: bash -euxo pipefail {0}
     - name: steps::cargo_install_nextest
       run: cargo install cargo-nextest --locked
       shell: bash -euxo pipefail {0}