deposit: Synchronize HTTP read timeout with deposit server

When the deposit loader downloads a deposited tarball, it calls the raw
endpoint of deposit private HTTP API. In production, the implementation
of that endpoint downloads a set of tarballs from an azure blob storage
and return an aggregated version of them.

It has been observed some HTTP read timeouts while downloading tarballs
from azure. Those have been fixed in swh-deposit!453 by increasing
the read timeout used to read data from azure.

However, there is still some deposit loader tasks that end up with error
as the read timeout used to query the raw endpoint of deposit private API
is twice lesser than the read timeout used to download from azure.
So ensure those HTTP read timeouts have the same value of 120 seconds.