Get arbitrary check passing (2.0) (#2710)

## Issue Addressed

NA

## Proposed Changes

This is a wholesale rip-off of #2708, see that PR for more of a description.

I've made this PR since @realbigsean is offline and I can't merge his PR due to Github's frustrating `target-branch-check` bug. I also changed the branch to `unstable`, since I'm trying to minimize the diff between `merge-f2f`/`unstable`. I'll just rebase `merge-f2f` onto `unstable` after this PR merges.

When running `make lint` I noticed the following warning:

```
warning: patch for `fixed-hash` uses the features mechanism. default-features and features will not take effect because the patch dependency does not support this mechanism
```

So, I removed the `features` section from the patch.

## Additional Info

NA


Co-authored-by: realbigsean <seananderson33@gmail.com>

crypto/bls/src/generic_aggregate_signature.rs

@@ -307,7 +307,7 @@ where
 }
 
 #[cfg(feature = "arbitrary")]
-impl<Pub, AggPub, Sig, AggSig> arbitrary::Arbitrary
+impl<Pub, AggPub, Sig, AggSig> arbitrary::Arbitrary<'_>
     for GenericAggregateSignature<Pub, AggPub, Sig, AggSig>
 where
     Pub: 'static,