Update provider.dart

[yoman07]

Fix for using shouldUpgradeAnonymous for Apple provider

Description

It fixes problem with updating anonymous account for apple provider.

Related Issues

Problem well described here:
Apple log in inconsistency problem

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]).
• All existing and new tests are passing.
• I updated/added relevant documentation (doc comments with ///).
• The analyzer (melos run analyze) does not report any problems on my PR.
• All unit tests pass (melos run test:unit:all doesn't fail).
• I read and followed the [Flutter Style Guide].
• I signed the [CLA].
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Breaking Change

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

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