Temporary fix for macOS runner upgrade crash loop. (#1304)

src/Runner.Listener/SelfUpdater.cs

@@ -74,10 +74,12 @@ namespace GitHub.Runner.Listener
                 await jobDispatcher.WaitAsync(token);
                 Trace.Info($"All running job has exited.");
 
+                // We need to keep runner backup around for macOS until we fixed https://github.com/actions/runner/issues/743
+#if !OS_OSX
                 // delete runner backup
                 DeletePreviousVersionRunnerBackup(token);
                 Trace.Info($"Delete old version runner backup.");
-
+#endif
                 // generate update script from template
                 await UpdateRunnerUpdateStateAsync("Generate and execute update script.");