Specify default host triple rather than default toolchain

Since the default host triple was still detected as that of the
runner outside the container.

With the default host triple set as desired, the default toolchain
should be inferred correctly from that as well.

Author: EliahKagan

.github/workflows/ci.yml

@@ -208,11 +208,11 @@ jobs:
           - container-arch: i386
             runner-arch: amd64
             runner-os: ubuntu-latest
-            toolchain: stable-i686-unknown-linux-gnu
+            host-triple: i686-unknown-linux-gnu
           - container-arch: arm32v7
             runner-arch: arm64
             runner-os: ubuntu-24.04-arm
-            toolchain: stable-armv7-unknown-linux-gnueabihf
+            host-triple: armv7-unknown-linux-gnueabihf
 
     runs-on: ${{ matrix.runner-os }}
 
@@ -241,7 +241,7 @@ jobs:
         run: |
           # Specify toolchain to avoid possible misdetection based on the 64-bit running kernel.
           curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs |
-            sh -s -- -y --default-toolchain ${{ matrix.toolchain }} --profile minimal
+            sh -s -- -y --default-host ${{ matrix.host-triple }} --profile minimal
       - name: Add Rust tools to path
         run: echo "PATH=$HOME/.cargo/bin:$PATH" >> "$GITHUB_ENV"
       - uses: Swatinem/rust-cache@v2