fix(core, ios): ensure iOS SDK version can be found from Package.swift

[russellwheatley]

Description

• Increased swift integration test timeout which was the reason why it was failing. It also matches the timeout set in Firestore PR: https://github.com/firebase/flutterfire/pull/13329/files#diff-61a085d0578afbe6a13da0c8926054ea59e83ce30bd655a6349e78afe7940351R127

• I was able to reproduce the bug on a throwaway Flutter app outside of Flutterfire. I tested by pointing to firebase_core on path with the fix and I was able to build successfully:

  

Related Issues

fixes https://github.com/firebase/flutterfire/issues/13726

Checklist

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• [ ] I read the Contributor Guide and followed the process outlined there for submitting PRs.
• [ ] My PR includes unit or integration tests for all changed/updated/fixed behaviors (See Contributor Guide).
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• [ ] I updated/added relevant documentation (doc comments with ///).
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Breaking Change

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• [ ] Yes, this is a breaking change.
• [ ] No, this is not a breaking change.

[kuhnroyal]

Tested this locally with Git dependency, no more build errors. Thanks!