[electrum] pinpoint packaging lib and specify hashes for MacOS build
Summary:
Bumping pyinstaller-hooks-contrib in D16719 introduced another indirect dependency for the build process on MacOS.
This change should have been included in that commit but was accidentaly stashed while testing.
Test Plan:
contrib/osx/make_osx
Check for no errors
Reviewers: #bitcoin_abc, Fabien
Reviewed By: #bitcoin_abc, Fabien
Differential Revision: https://reviews.bitcoinabc.org/D16725