GHA: Add ppa:ubuntu-toolchain-r/test for gcc-10

.github/workflows/build-linux.yml

@@ -85,7 +85,7 @@ jobs:
           apt-get update
           apt-get install -y build-essential git wget curl sudo unzip zip openjdk-11-jdk autoconf libfreetype6-dev libcups2-dev libx11-dev libxext-dev libxrender-dev libxrandr-dev libxtst-dev libxt-dev libasound2-dev libffi-dev file binutils libfontconfig-dev
           # If we really need gcc-10, we can get it from this PPA:
-          #sudo add-apt-repository ppa:ubuntu-toolchain-r/test
+          sudo add-apt-repository ppa:ubuntu-toolchain-r/test
 
       - name: 'Checkout the JDK source'
         uses: actions/checkout@v3