fix: changes regex for basic auth to be case-insensitive and adds tests for mixed case prefixes

[caiubi]

Summary

The RFC for basic authentication specifies that the "scheme" should be matched case-insensitively, so I changed the regex and added some specs.

Other Information

N/A

[nbulaj]

I checked OAuth RFC which refers HTTP Authentication RFC and it tells about case-insensitive auth token as well. So LGTM 👍

[Copilot]

Pull request overview

This pull request updates the Basic authentication header parsing to be case-insensitive, aligning with RFC 7617 specifications. The regex pattern is modified from /^Basic (.*)/m to /^Basic (.*)/im and comprehensive test coverage is added.

Changes:

• Modified regex pattern in from_basic method to use case-insensitive matching with the i flag
• Added test cases for lowercase 'basic' and mixed case 'BaSiC' authentication prefixes

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
lib/doorkeeper/oauth/client/credentials.rb	Updated regex pattern to add case-insensitive flag (i) for matching the "Basic" authentication scheme
spec/lib/oauth/client/credentials_spec.rb	Added two new test cases to verify case-insensitive matching works with lowercase and mixed case variations

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[nbulaj]

Hello @caiubi .Sorry for the delay. Can you please also add a changelog entry and squash commits then ? 🙏 Thanks!

[caiubi]

It's done! 😄