fix(scheme): make scheme comparison case insensitive

[char0n]

As per RFC7235 auth scheme is case insensitive.

2.1. Challenge and Response

HTTP provides a simple challenge-response authentication framework
that can be used by a server to challenge a client request and by a
client to provide authentication information. It uses a case-
insensitive token as a means to identify the authentication scheme,
followed by additional information necessary for achieving.

https://tools.ietf.org/html/rfc7235#section-2.1

Refs #1531, #1473
Refs OAI/OpenAPI-Specification#1876
Refs swagger-api/swagger-ui#5965

Types of changes

• No code changes (changes to documentation, CI, metadata, etc)
• Dependency changes (any modification to dependencies in package.json)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

[char0n]

@hkosova thanks for noticing it. It'll issue a separate PR for correcting this in rest of the tests that we have.