Values may not be strings

[Artistan]

Enabled Guzzle Client and caused found that this would error out.

return new TwilioGuzzleClient(new GuzzleClient(['handler' => $stack]));

responseHeaders example:

{
  "Connection": [
    "keep-alive"
  ],
  "Content-Length": [
    "2136"
  ],
  "Content-Type": [
    "application/json;charset=utf-8"
  ],
  "Date": [
    "Mon, 02 Feb 2026 20:46:35 GMT"
  ],
  "Strict-Transport-Security": [
    "max-age=31536000"
  ],
  "Twilio-Concurrent-Requests": [
    "1"
  ],
  "Twilio-Request-Duration": [
    "0.024"
  ],
  "Twilio-Request-Id": [
    "***"
  ],
  "Vary": [
    "Origin"
  ],
  "Via": [
    "1.1 ***.cloudfront.net (CloudFront)"
  ],
  "X-API-Domain": [
    "api.twilio.com"
  ],
  "X-Amz-Cf-Id": [
    "***=="
  ],
  "X-Amz-Cf-Pop": [
    "***-P5"
  ],
  "X-Cache": [
    "Miss from cloudfront"
  ],
  "X-Home-Region": [
    "us1"
  ],
  "X-Powered-By": [
    "AT-5000"
  ],
  "X-Shenanigans": [
    "none"
  ]
}

Fixes

A short description of what this PR does.

Checklist

• I acknowledge that all my contributions will be made under the project's license
• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have read the Contribution Guidelines and my PR follows them
• I have titled the PR appropriately
• I have updated my branch with the main branch
• I have added tests that prove my fix is effective or that my feature works
• I have added the necessary documentation about the functionality in the appropriate .md file
• I have added inline documentation to the code I modified

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