docs: don't use IncomingRequest::$uri

[kenjis]

Description

• don't use IncomingRequest::$uri in the user guide. See IncomingRequest property $uri is public and should be protected #5344

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