Fix CI by installing risc0

Author: ozankaymak

.github/workflows/CI.yml

@@ -37,6 +37,8 @@ jobs:
     - uses: actions/checkout@v4
     - name: Build guests
       run: |
+        curl -L https://risczero.com/install | bash
+        rzup install cargo-risczero 2.0.2
         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