Vibe.d sometimes still timeouts

[wilzbach]

e.g. https://buildkite.com/dlang/phobos/builds/844#b0d85adf-6754-43e8-8225-968ad7262794

Probably related to the low network speed on the agents (see e.g. #347).

Not sure how we can solve this for now. More retries? Higher timeouts?