Workflow for labeled iOS PRs in 5.x branch

[asenyaev]

Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

• I agree to contribute to the project under Apache 2 License.
• To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
• The PR is proposed to the proper branch
• There is a reference to the original bug report and related work
• There is accuracy test, performance test and test data in opencv_extra repository, if applicable
  Patch to opencv_extra has the same branch name.
• The feature is well documented and sample code can be built with the project CMake

[fengyuentau]

👍

[asenyaev]

Fixed parsing a label platform: ios/osx.

[fengyuentau]

It seems opencv building with ffmpeg on macOS-ARM64 can be buggy. The unit tests in videoio module can be stuck and timed out eventually.

[asenyaev]

@fengyuentau, yes, I see. I will add stuck tests in gtest filter.