Replace URI string casts

[MGatner]

Description
Due to the following:

CodeIgniter4/system/HTTP/URI.php

Lines 681 to 702 in 7eef1f7

	// Check if this is an internal URI
	$config = config('App');
	$baseUri = new self($config->baseURL);
	// If the hosts matches then assume this should be relative to baseURL
	if ($this->getHost() === $baseUri->getHost())
	{
	// Check for additional segments
	$basePath = trim($baseUri->getPath(), '/') . '/';
	$trimPath = ltrim($path, '/');
	if ($basePath !== '/' && strpos($trimPath, $basePath) !== 0)
	{
	$path = $basePath . $trimPath;
	}
	// Check for forced HTTPS
	if ($config->forceGlobalSecureRequests)
	{
	$scheme = 'https';
	}
	}

... URI::__toString() is only suitable for project URLs, because any partial match of baseURL will be a false positive. Following on #4715, this PR removes the remaining string casts of URI when they are not explicitly a project URI.

Checklist:

• Securely signed commits
• Component(s) with PHPdocs
• Unit testing, with >80% coverage
• n/a User guide updated
• Conforms to style guide