schemathesis: [BUG] Generating invalid HTTP headers

Describe the bug Schemathesis generates headers like:

x-api-key: \x80

The \x80 character is not a part of ISO-8859-1 (AKA Latin-1). This is an issue because according to the HTTP 1.1 standard, all HTTP headers are encoded with ISO-8859-1. This means that my tests will always fail because of something I can’t actually control.

To Reproduce

1. In your OpenAPI Schema, add a security schema:

     securitySchemes:
       ApiKey:
         type: apiKey
         in: header
         name: x-custom-api-key-header
   security:
     - ApiKey: []
   

2. Run Schemathesis

Expected behavior

I expect Schemathesis to not generate things that are unsupported due to the HTTP spec. By definition, these things will not have stable behaviour, so it’ll be impossible to test with Schemathesis.

Environment (please complete the following information):

• OS: Windows 10
• Python version: 3.9.2
• Schemathesis version: 3.6.3
• Spec version: Open API 3.0.3