depsbuild(deps): Bump `zcash_client_backend` for `zebra-scan`

[oxarbitrage]

Motivation

We want to upgrade zcash_client_backend for the zebra-scan crate.

I believe the combination of https://github.com/ZcashFoundation/zebra/pull/8522 and this PR (which is based in https://github.com/ZcashFoundation/zebra/pull/8560) will make all the builds and tests to pass. That is what i am going to be trying next.

However, there are some open questions on this PR that might need discussion. I will add review comments in the places i am most concerned.