CI: ubuntu-toolchain-r/test repository will be removed (#14641)

* CI: ubuntu-toolchain-r/test repository will be removed

The ubuntu-toolchain-r/test PPA will be removed from Ubuntu images.
The images rollout process will start on May 6 and take 3-4 days.
Mitigation ways

The repository can still be added manually in runtime by calling to following commands:

sudo add-apt-repository ppa:ubuntu-toolchain-r/test -y
sudo apt-get update -y

* fixup: add a note what this repo is for

Signed-off-by: Philip H <47042125+pheiduck@users.noreply.github.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 98f8d8a..0307b45 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -131,6 +131,9 @@
       - name: Install gcc-${{ env.GCC_VER }}
         if:  matrix.compiler == 'gcc'
         run: |
+          # ubuntu-toolchain-r/test PPA for gcc-13 compiler
+          sudo add-apt-repository ppa:ubuntu-toolchain-r/test -y
+          sudo apt-get update -y
           sudo apt-get install -y gcc-${{ env.GCC_VER }}:${{ matrix.architecture }}
           sudo update-alternatives --install /usr/bin/gcc gcc /usr/bin/gcc-${{ env.GCC_VER }} 100
           sudo update-alternatives --set gcc /usr/bin/gcc-${{ env.GCC_VER }}