pin the version of geth used in CI

.github/workflows/test.yml

@@ -101,7 +101,7 @@ jobs:
         run: |
           sudo add-apt-repository -y ppa:ethereum/ethereum
           sudo apt-get update
-          sudo apt-get install -y ethereum protobuf-compiler
+          sudo apt-get install -y ethereum=1.15.11+build31083+noble protobuf-compiler
 
       - name: Install Geth on macOS
         if: matrix.os == 'macos-14'