ci: add ad-hoc app signature for macos target

[Beerosagos]

Before asking for reviews, here is a check list of the most common things you might need to consider:

• updating the Changelog
• writing unit tests
• checking if your changes affect other coins or tokens in unintended ways
• testing on multiple environments (Qt, Android, ...)
• having an AI review your changes

[Beerosagos]

@benma this seems to fix the issue for me and @thisconnect. Here it is quite easy to test, since the previous commit artifact is blocked by mac os, but maybe it would be better to bring it directly on master. wdyt?

[benma]

I am confused why this is the right path. Isn't the repo and build in {{github.workspace}}, which is the working dir?

Doesn't a relative path work like in other jobs then? I.e. simply frontends/qt/build/osx/BitBox.app.

If not, it would be good to use go env GOPATH instead of $HOME/go.

[benma]

@benma this seems to fix the issue for me and @thisconnect. Here it is quite easy to test, since the previous commit artifact is blocked by mac os, but maybe it would be better to bring it directly on master. wdyt?

I agree this should be in master too.

[benma]

Also please add some details to the commit message body.