fix #308281 : Blank upload dialog on MacOS Catalina + collect_artifacts

[AntonioBL]

Resolves: https://musescore.org/en/node/308281

Apparently, QtWebEngine requires additional permissions to run under MacOS 10.15, see https://forum.qt.io/post/526704

• I signed CLA
• I made sure the code in the PR follows the coding rules
• I made sure the code compiles on my machine
• I made sure there are no unnecessary changes in the code
• I made sure the title of the PR reflects the core meaning of the issue you are solving
• I made sure the commit message(s) contain a description and answer the question "Why do those changes fix that particular issue?" or "Why are those changes really necessary as improvements?"
• I made sure the commit message title starts with "fix #424242:" if there is a related issue
• [ N/A ] I created the test (mtest, vtest, script test) to verify the changes I made

[BernardGreenberg]

I, the original plaintiff, have verified that Antonio's executable really does solve the problem I reported.

[AntonioBL]

( Thanks, BSG 😄 )

Additional note for the developers running MacOS Catalina:
I had to downgrade the XCode in the Github actions otherwise the artifacts would crash on start because of something Apple did to their version of OpenGL in 10.15 sdk.
See:
https://www.geeks3d.com/hacklab/20191214/geexlab-0-29-9-1-released-with-macos-10-15-catalina-support/
TheInfiniteKind/appbundler#70
https://github.com/google/filament/pull/1959/files
So, at the moment, a build of MuseScore made with the latest XCode will most probably crash on startup because of the "OpenGL can be called from the main thread only" limitation.

[BernardGreenberg]

This (OpenGL) issue looks like a disaster; does that cripple all Qt development toward Catalina, or only 5.9?

[AntonioBL]

This (OpenGL) issue looks like a disaster; does that cripple all Qt development toward Catalina, or only 5.9?

Well, I really don't know for sure. I think Qt 5.14 could have some improvements in this field, but I didn't test it.

[anatoly-os]

Manually merged to master (8f0f185)