This is the time of the year Apple breaks our mac builds, as usual.
mac now has its own "binaries" requirements. This allows us to use
an older version of PyQt5 in the mac binaries. For some reason
if we bundle newer PyQt5, the built app will not start on macOS 11
(but will on older macOS).
related: #6461
in particular, see https://github.com/spesmilo/electrum/issues/6461#issuecomment-713888921
