Fixes #362

Notice

@hannesa2 this cannot be fully tested in the forked PR because the CI step with the change will be skipped.

I partially tested it though in #377 by enabling the Prepare artifact step. The DMG files work correctly, but the GitX app won't run due to the lack of signing (which we fixed already in #376).

If needed to confirm a full test, please use an origin PR to do an integration test with xcodebuild -exportArchive.

• The generated DMG files should work correctly in both platforms. (This works.)
• Dragging GitX onto Applications should install it. Finder may ask to replace existing copy. (This works.)
• Installed GitX should run without issues or crashes. (This doesn't work in forked PR due to lack of signing.)

Screenshot