fix(ci): add libbrotli-dev for Qt6Network dependency

Static Qt 6.9 was built with brotli support, which requires
libbrotli-dev at configure time. Previously pulled in indirectly
via PPA apt upgrade, now missing in clean Ubuntu 20.04.

Author: ZnPdCo

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

@@ -57,7 +57,7 @@ jobs:
           apt install -y build-essential ninja-build pkgconf bash
           apt install -y libgl1-mesa-dev libglu1-mesa-dev
           apt install -y libfontconfig1-dev libfreetype6-dev libx11-dev libx11-xcb-dev libxext-dev libxfixes-dev libxi-dev libxrender-dev libxcb1-dev libxcb-glx0-dev libxcb-keysyms1-dev libxcb-image0-dev libxcb-shm0-dev libxcb-icccm4-dev libxcb-sync0-dev libxcb-xfixes0-dev libxcb-shape0-dev libxcb-randr0-dev libxcb-render-util0-dev  libxcb-xinerama0-dev libxkbcommon-dev libxkbcommon-x11-dev
-          apt install -y libharfbuzz-dev libsm-dev libdrm-dev
+          apt install -y libharfbuzz-dev libsm-dev libdrm-dev libbrotli-dev
           apt install -y '^libxcb.*-dev' libx11-xcb-dev libglu1-mesa-dev libxrender-dev libxi-dev libxkbcommon-dev libxkbcommon-x11-dev
           apt install -y bubblewrap
       - name: Install Qt