Update build.yml

Author: actboy168

.github/workflows/build.yml

@@ -42,15 +42,19 @@ jobs:
           add-apt-repository -y ppa:git-core/ppa # For git>=2.18.
           apt-get update
           apt-get install -y sudo git gcc-9 g++-9
-          update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-9 100
-          update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-9 100
 
       - name: Install aarch64-linux-gnu
         if: ${{ matrix.platform == 'linux-arm64' }}
         run: |
           apt-get update
           apt-get install -y gcc-aarch64-linux-gnu g++-aarch64-linux-gnu
 
+      - name: Prepare container
+        if: ${{ matrix.target == 'linux' }}
+        run: |
+          update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-9 100
+          update-alternatives --install /usr/bin/g++ g++ /usr/bin/g++-9 100
+
       - uses: actions/checkout@v3
         with:
           submodules: recursive