test: remove $request->uri and fix incorrect assertions

[kenjis]

Description
See #5344

• IncomingRequest::$uri will be protected.
• $request->getUri()->getPath() does not start with /. IncomingRequest::$uri is a bit different from a normal URI object.
  

  CodeIgniter4/system/HTTP/IncomingRequest.php

  Lines 60 to 71 in a3eedf4

  	* The URI for this request.
  	*
  	* Note: This WILL NOT match the actual URL in the browser since for
  	* everything this cares about (and the router, etc) is the portion
  	* AFTER the script name. So, if hosted in a sub-folder this will
  	* appear different than actual URL. If you need that use getPath().
  	*
  	* @TODO should be protected. Use getUri() instead.
  	*
  	* @var URI
  	*/
  	public $uri;

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