fix: Update thumbprints input variable to be a list with 2 items as default

[jreslock]

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📒 Description

🕶️ Types of changes

• [ ] Core
• [ ] Bugfix
• [ ] New feature
• [X] Enhancement/optimization
• [ ] Documentation
• [ ] Dependencies

🤯 List of changes

GitHub has 2 thumbprints and the input variable should have them both as a default value.

Also fixing tflint warnings

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Checklist

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[jreslock]

This is a duplicate of https://github.com/terraform-module/terraform-aws-github-oidc-provider/pull/35