docs: Relax the expectations of HW CI farms.

We've been doing pretty well at around half an hour per pipeline, no need
to be too harsh.

Reviewed-by: Eric Engestrom <eric@engestrom.ch>
Reviewed-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5510>
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