fix(ci): remove savoury1 PPA to resolve dependency conflict

The PPA recently added freetype 2.12.1 for focal, which conflicts
with Ubuntu 20.04's libfontconfig1-dev after .
Ubuntu 20.04 ships cmake 3.16.3 which satisfies the project requirement.

Author: ZnPdCo

.github/workflows/linux-static-qt6.yml

@@ -43,10 +43,6 @@ jobs:
       - name: Install Build Essentials
         run: |
           apt update
-          apt install -y software-properties-common
-          add-apt-repository ppa:savoury1/build-tools
-          apt update
-          apt upgrade -y
           apt install -y build-essential git perl cmake ninja-build wget
       - name: Checking out sources
         uses: actions/checkout@v6