fix typo in KubernetesCredentials

[blakerosenthal]

Reference Issues or PRs

Fixes typo and removes typos: ignore from src/_nebari/stages/infrastructure/__init__.py as described in #2597.

I verified that no additional changes are needed for the upgrade step since this pydantic model is only used as an output.

Fixes #2597

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• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds a feature)
• Breaking change (fix or feature that would cause existing features not to work as expected)
• Documentation Update
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Build related changes
• Other (please describe):

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