🧪 Add edge case test for string error-codes in Response

[rowan-m]

🎯 What: The testing gap addressed
A missing edge case test for the Response class when error-codes are passed as a string (e.g., {"success": false, "error-codes": "bad-request"}) instead of the expected array format.

📊 Coverage: What scenarios are now tested
The ResponseTest::testFromJson method now includes a scenario that verifies handling of string error-codes in the JSON response. If error-codes is not an array, the parser falls back to returning an array containing ReCaptcha::E_UNKNOWN_ERROR, maintaining correct expected types.

✨ Result: The improvement in test coverage
The test coverage now protects the explicit is_array($responseData['error-codes']) type safety check in Response::fromJson. It guarantees the code safely ignores invalid formats and handles the error gracefully without throwing type errors downstream.

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PR created automatically by Jules for task 3535967434115694764 started by @rowan-m

[google-labs-jules]

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[coveralls]

coverage: 100.0%. remained the same
when pulling 5424a3b on test/edge-case-string-error-codes-3535967434115694764
into 188ef61 on main.