Fix OSX SDK pinning for qt-main on arm64

[andfoy]

Checklist

• Used a personal fork of the feedstock to propose changes
• Bumped the build number (if the version is unchanged)
• Reset the build number to 0 (if the version changed)
• Re-rendered with the latest conda-smithy (Use the phrase @conda-forge-admin, please rerender in a comment in this PR for automated rerendering)
• Ensured the license file is being packaged.

[conda-forge-linter]

Hi! This is the friendly automated conda-forge-linting service.

I just wanted to let you know that I linted all conda-recipes in your PR (recipe) and found it was in an excellent condition.

[andfoy]

@isuruf, is this one ready?

[hmaarrfk]

Sorry for letting this go. I guess people forget to check up on all PRs. is this still relevant today?

[andfoy]

This was before updating Qt to 5.15.14, so I think this can be marked as not needed anymore?

[varlackc]

There seem to be some conflicts in the current branch.
As soon as the conflicts are resolve, we should be ready to merge.