Adds Mac iOS Engine target to flutter/recipes CQ. This will ensure that changes to flutter/recipes pass on the Mac iOS Engine target before landing.

The recipes code has a temporary workaround to resolve a P0 related to Mac iOS Engine. A proper workaround has been readied, but the Mac iOS Engine target fails to build and test when run as an individual tryjob in a CL. This is because running it individually does not pass it the necessary config. This change will make the Mac iOS Engine target run for every flutter/recipes CL and with proper config, which will let us validate changes that affect it.

flutter/flutter#111226
flutter/flutter#111193

Pre-launch Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the Tree Hygiene wiki page, which explains my responsibilities.
• I read and followed the Flutter Style Guide and the C++, Objective-C, Java style guides.
• I listed at least one issue that this PR fixes in the description above.
• I added new tests to check the change I am making or feature I am adding, or Hixie said the PR is test-exempt. See testing the engine for instructions on
  writing and running engine tests.
• I updated/added relevant documentation (doc comments with ///).
• I signed the CLA.
• All existing and new tests are passing.

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