Make validCardBrands field optional

[artsiom-dorakhau]

Description

Docs say validCardBrands is optional, but the type requires it. This PR fixes that.

Motivation and Context

How Has This Been Tested?

Screenshots (if appropriate):

Types of Changes

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.