1. If HTTP_HOST is set in $server parameter of request method, it overrides hostname part of URI.
   https://github.com/symfony/BrowserKit/blob/292751e7b351b1e7d400c7529c07d713af2ff92a/Client.php#L299
2. HTTP_HOST header is set to hostname part of URI.
   https://github.com/symfony/BrowserKit/blob/292751e7b351b1e7d400c7529c07d713af2ff92a/Client.php#L313
3. HTTP_HOST set with setServerParameters is completely ignored.

The first action is completely unexpected and should be removed.
The second action should only be used if HTTP_HOST is not set in $server.
Currently it is set to localhost by default
which is never used, so it should be removed.