ci(v8): install upstream Rust target explicitly

.github/workflows/v8-canary.yml

@@ -306,18 +306,21 @@ jobs:
           python-version: "3.11"
           architecture: x64
 
-      - name: Set up rusty_v8 Rust toolchain
-        uses: dtolnay/rust-toolchain@a0b273b48ed29de4470960879e8381ff45632f26 # 1.93.0
-        with:
-          toolchain: "1.91.0"
-          targets: ${{ matrix.target }}
-
       - name: Set up Codex Rust toolchain for Cargo smoke
         uses: dtolnay/rust-toolchain@a0b273b48ed29de4470960879e8381ff45632f26 # 1.93.0
         with:
           toolchain: "1.93.0"
           targets: ${{ matrix.target }}
 
+      - name: Install rusty_v8 Rust toolchain
+        env:
+          TARGET: ${{ matrix.target }}
+        shell: bash
+        run: |
+          set -euo pipefail
+          rustup toolchain install 1.91.0 --profile minimal --no-self-update
+          rustup target add --toolchain 1.91.0 "${TARGET}"
+
       - name: Write upstream submodule status
         shell: bash
         working-directory: upstream-rusty-v8