server: allow private media URLs in the vision tests [no ci] (#32167)
The vision tests download their images from huggingface.co, which
resolves to a private address on the runners inside the HF network.
The media URL check refuses it with "host is not a public address"
and the server-cuda job fails.
The vision fixture enables media_allow_private_urls. The private
address check keeps its own coverage in
test_vision_image_url_private_address.