I don't think you really need a Mac – any browser running on WebKit should get you 95% there. GNOME Web on Linux, for example.
Also, using non-Safari WebKit for everyday testing (will my newest commit break it? should I fix something before I send the PR?) but using the proper Safari for more thorough testing (e. g. before public releases, or when a bugreport can't be reproduced otherwise) is an option too.