ci: drop ubuntu 18.04 support #882

Job	Run time
SaveVersion	7s
Mac (macos, 12, 5.15.2, x64, macos-qt5, -DKLOGG_OSX_DEPLOYMENT_TARGET=11.7)	1m 41s
Windows (windows, 2022, 6.7.3, qt5compat, x64, -x64, windows-x64-qt6)	1m 32s
Mac (macos, 12, 6.7.3, qt5compat, x64, macos-qt6, -DKLOGG_OSX_DEPLOYMENT_TARGET=11.7)	1m 24s
Linux (oraclelinux, 8, x64, yum install -y --setopt tsflags=test /usr/local/klogg*.rpm, RPM, orac...	1m 38s
Windows (windows, 2022, 5.15.2, x64, -x64, windows-x64-qt5)	1m 30s
Linux (ubuntu_focal, 20.04, x64, apt-get update && apt install --dry-run /usr/local/klogg*.deb, D...	1m 39s
Windows (windows, 2022, 5.15.2, x86, win32_msvc2019, windows-x86-qt5)	1m 30s
Linux (ubuntu_jammy, 22.04, x64, apt-get update && apt install --dry-run /usr/local/klogg*.deb, D...	1m 39s
Linux (ubuntu_noble, 24.04, x64, apt-get update && apt install --dry-run /usr/local/klogg*.deb, D...	6s
Linux (ubuntu_appimage, 20.04, x64, appimage, AppImage, docker/ubuntu20.04_qt5.15, variar/klogg_u...	5s
	12m 51s

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