I have only seen the issue in DuckDuckGo. Perhaps Google and Bing don't show results with raw IP addresses.
Looking at the doc's page source code in the browser, the robots meta tag doesn't seem to be set.

AFAIK, something like <meta name="robots" content="noindex nofollow" /> should fix the issue. I imagine it would be preferable to set it to a different value for the official docs, though.

Results for "judge0 api documentation":

• DuckDuckGo
• Google
• Bing