Fix `TestClientWebsocketLargeMessage` flaky test

[JonathanOppenheimer]

See https://github.com/ava-labs/coreth/actions/runs/17594831212/job/49984435300?pr=1184

[JonathanOppenheimer]

See here as well: https://github.com/ava-labs/subnet-evm/actions/runs/17744446603/job/50426127045?pr=1728

[JonathanOppenheimer]

Here is another one: https://github.com/ava-labs/subnet-evm/actions/runs/17919301530/job/50949703934?pr=1740