ci: disable cache-bin to fix flaky macOS builds (#411)

Swatinem/rust-cache with cache-bin: true (the default) caches
~/.cargo/bin, which contains rustup proxy binaries. On macOS, rustup
uses RUSTUP_PERMIT_COPY_RENAME=1, so these proxies are copies of the
rustup binary. When the cache restores stale copies, they can resolve
to rustup-init instead of the proper cargo proxy, causing:

  error: unexpected argument 'test' found
  Usage: rustup-init[EXE] [OPTIONS]

Setting cache-bin: false prevents caching the bin directory, letting
rustup manage its own proxy binaries correctly.

Author: rcoh

.github/actions/rust-build/action.yml

@@ -18,6 +18,7 @@ runs:
         - uses: Swatinem/rust-cache@v2
           with:
               save-if: ${{ inputs.save-if }}
+              cache-bin: "false"
         - name: Enable perf_event_open and kallsyms for tests
           if: runner.os == 'Linux'
           shell: bash