Add correct type for $jwt, should be JWT

[jose-ochoa]

For #2641

This pull request includes changes to the Verify class in the src/AccessToken/Verify.php file to improve type safety by updating the type hints for the jwt property and constructor parameter.

Type safety improvements:

• src/AccessToken/Verify.php: Changed the type hint of the jwt property from \Firebase\JWT\JWT to JWT.
• src/AccessToken/Verify.php: Updated the type hint of the jwt parameter in the constructor from ?string to ?JWT.

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