Fix CI: Specify rust version

Author: ozankaymak

.github/workflows/CI.yml

@@ -39,6 +39,7 @@ jobs:
       run: |
         curl -L https://risczero.com/install | bash
         rzup install cargo-risczero 2.0.2
+        rzup install rust 1.85.0
         REPR_GUEST_BUILD=1 BITCOIN_NETWORK=mainnet cargo build -p header-chain-circuit --release
         REPR_GUEST_BUILD=1 BITCOIN_NETWORK=mainnet cargo build -p final-spv-circuit --release