ci(ios): update workflow w/ iOS 15

[erisu]

Platforms affected

iOS

Motivation, Context & Description

Previously all iOS test appeared to run only on iOS 14.4.

This PR:

• Update GitHub Actions workflow to ensure that each defined iOS version was being tested correctly.
• Included iOS 15.x to the workflow.

Testing

• CI

Checklist

• I've run the tests to see all new and existing tests pass
• I added automated test coverage as appropriate for this change
• Commit is prefixed with (platform) if this change only applies to one platform (e.g. (android))
• If this Pull Request resolves an issue, I linked to the issue in the text above (and used the correct keyword to close issues using keywords)
• I've updated the documentation if necessary

[timbru31]

iOS 15 failed

[erisu]

The iOS failures are actual issues that need to be reviewed and fixed under a separate PR.

The goal of this PR was not to fix the iOS issues that were already existing but to accurately report what platform is breaking.

After the last run of this PR, you can see iOS 12 is also failing. Since failures will stop the entire workflow, all iOS versions may fail.

I will go ahead and merge in this PR to resolve the inaccurate testing and will also open a bug ticket for the current issues displayed in the log.