glib-macros: add test macro for async-glib-context tests#1521

sdroege merged 1 commit intogtk-rs:mastergtk-rs/gtk-rs-core:masterfrom

BiagioFesta:wip/bfesta/macro-test-asyncBiagioFesta/gtk-rs-core:wip/bfesta/macro-test-asyncCopy head branch name to clipboard