Improve error message when encountering unexpected content-type headers

[simonjbeaumont]

Motivation

When the server response has a content-type header that does not conform to the OpenAPI document, we currently throw an error. However, this error presents itself in a very confusing manner: it prints Unexpected Content-Type header: application/json, where `application/json is the expected content-type. At best, this is ambiguous and potentially misleading.

Modifications

• Extend case RuntimeError.unexpectedContentTypeHeader with both the expected and received content-type associated values.
• Update the printed description to include both the expected and received content-type header values.

Result

When an unexpected content-type is received, the error message is clearer.

Test Plan

Updated the existing test that expects an error to check the error and that the error values are provided in the correct order.

[czechboy0]

Nice quality of life improvement! 👏