There seems to be a pretty high frequency of timeouts right now on mac ci bots.
Examples:
From #150585
https://github.com/flutter/flutter/pull/150585/checks?check_run_id=26535171974
https://github.com/flutter/flutter/pull/150585/checks?check_run_id=26535172379

From #150614
https://github.com/flutter/flutter/pull/150614/checks?check_run_id=26520636606
https://github.com/flutter/flutter/pull/150614/checks?check_run_id=26520632867

From #150517
https://github.com/flutter/flutter/pull/150517/checks?check_run_id=26528249189
https://github.com/flutter/flutter/pull/150517/checks?check_run_id=26528248334