Make sure add-apt-repository is available.

.github/workflows/pr_build.yml

@@ -184,15 +184,16 @@ jobs:
       run: |
         if [[ "${{ matrix.os }}" =~ "Ubuntu" || "${{ matrix.os }}" =~ "Debian" ]]; then
 
-          echo "Adding Toolchain test PPA"
-          add-apt-repository ppa:ubuntu-toolchain-r/test
-
           echo "Updating apt repository index"
           sudo apt update || exit 1
 
           echo "Installing apt packages"
           sudo apt install -y ${{ matrix.apt-dependencies }} || exit 1
 
+          echo "Adding Toolchain test PPA"
+          apt install -y software-properties-common
+          add-apt-repository ppa:ubuntu-toolchain-r/test
+
           echo "Installing gcc-13"
           apt install -y gcc-13 g++-13 || exit 1