[ci] Increase deprecation check minimum to iOS 15

[jmagman]

I tried this in #7542 and abandoned it because of the integration_test deprecation, but it's probably best to exclude it for now and still get the checks on the rest of the packages.

Exclude integration_test from deprecation checks until flutter/flutter#154365 is completed.

Last bump at #7431

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[jmagman]

Closing in favor of #9431