refactor: use baseURI instead of base_uri

[paulbalandan]

Description
Fixes #9265
Replaces and closes #9280

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[paulbalandan]

The test is useless because (1) in PHP, arrays with duplicate keys always retains the last key, and (2) CURLRequest::parseOptions() only checks for baseURI key not base_uri.