Update macOS build pipeline to 0.80

Notable updates include:

• latest GTK 3.24.42 for macOS specific fixes
• update Poppler to the last version supporting macOS 10.13 High Sierra
• add tinycss2 to enable/fix the tests requiring it
• replace the unmaintained pkg-config with pkgconf in the build infrastructure as it no longer builds on newest macOS
• backport the newer dmg background which contains the instructions to remove the quarantine flag