Update develop to patch-polkadot-sdk

Allows us to finally remove the old `serai-dex/substrate` repository _and_
should have CI pass without issue on `develop` again.

The changes made here should be trivial and maintain all prior
behavior/functionality. The most notable are to `chain_spec.rs`, in order to
still use a SCALE-encoded `GenesisConfig` (avoiding `serde_json`).

processor/src/tests/cosigner.rs

@@ -118,7 +118,7 @@ fn test_cosigner() {
         assert_eq!(signed_block, block);
         assert!(Public::from_raw(keys[&participant_one].group_key().to_bytes()).verify(
           &cosign_block_msg(block_number, block),
-          &Signature(signature.try_into().unwrap())
+          &Signature::from(<[u8; 64]>::try_from(signature).unwrap())
         ));
       }
       _ => panic!("didn't get cosigned block back"),