Update Boost used in system tests

Author: offa

.github/workflows/systemtest.yml

@@ -36,7 +36,9 @@ jobs:
       - name: Setup
         run: |
           script/ci_setup.sh
-          apt-get install -y libboost-system-dev
+          add-apt-repository ppa:nicola-onorata/toolchain
+          apt-get update
+          apt-get install -y boost1.81
       - name: Build
         run: |
           cmake --preset conan-release