Update build.yml

Author: actboy168

.github/workflows/build.yml

@@ -37,7 +37,13 @@ jobs:
         if: ${{ matrix.target == 'linux' }}
         run: |
           apt-get update
-          apt-get install -y gcc git
+          apt-get install -y software-properties-common
+          add-apt-repository -y ppa:ubuntu-toolchain-r/test # For gcc-9 and g++-9
+          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' }}