[Key Vault] Add default value for inner_error

[mccoyp]

Description

#41965 handled the edge case where inner_error is None, but didn't introduce a default value for the parameter; the model shouldn't be created by users, so the _from_error_bundle method should be the only place where a CertificateOperationError is constructed. However, for consistency with the type hint and to prevent unnecessary errors, this adds a default None value for the argument.

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

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• Title of the pull request is clear and informative.
• There are a small number of commits, each of which have an informative message. This means that previously merged commits do not appear in the history of the PR. For more information on cleaning up the commits in your PR, see this page.

Testing Guidelines

• Pull request includes test coverage for the included changes.

[Copilot]

Pull request overview

This PR updates the Key Vault Certificates public model CertificateOperationError to make its inner_error parameter optional by providing a default value of None, aligning runtime behavior with its type hint and preventing unnecessary instantiation errors when no inner error is present.

Changes:

• Add a default value (None) for the inner_error parameter in CertificateOperationError.__init__.

[mccoyp]

/check-enforcer override

CI failures are unrelated, though they should be addressed soon in a different PR.

[mccoyp]

/check-enforcer override