Clang: Install Cap'n Proto packages

Required since bitcoin/bitcoin#31802 was merged.

Author: hebasto

.github/workflows/clang.yml

@@ -45,7 +45,7 @@ jobs:
           sudo apt-get update
           LLVM_VERSION=$(apt-cache search --names-only '^clang-[0-9]+$' | sort -V | tail -1 | cut -f1 -d" " | cut -f2 -d"-" )
           echo "LLVM_VERSION=${LLVM_VERSION}" >> "$GITHUB_ENV"
-          sudo apt-get install clang-${LLVM_VERSION} ${{ matrix.configuration.dependencies }} libboost-dev libevent-dev libsqlite3-dev libzmq3-dev systemtap-sdt-dev
+          sudo apt-get install --no-install-recommends clang-${LLVM_VERSION} ${{ matrix.configuration.dependencies }} libboost-dev libevent-dev libsqlite3-dev libcapnp-dev capnproto libzmq3-dev systemtap-sdt-dev
 
       - name: Clang version
         run: clang-${LLVM_VERSION} -v