Fix Sequence Tests

[n7studios]

Summary

Fixes the create/update/delete sequence email test since the API changes rightly no longer permit setting a position of an existing email in a sequence to one that already exists.

1) ConvertKitAPIKeyTest::testCreateGetUpdateAndDeleteSequenceEmail
GuzzleHttp\Exception\ClientException: Client error: `PUT [https://api.kit.com/v4/sequences/1030824/emails/10087666`](https://api.kit.com/v4/sequences/1030824/emails/10087666%60) resulted in a `422 Unprocessable Content` response:
{"errors":["position 1 is already taken in this sequence"]}

Testing

Existing tests pass.

Checklist

• I have written a test and included it in this PR
• I have run all tests and they pass
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• The code passes when running PHPStan
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