Try and fix the Linux build.

Author: davidgiven

.github/workflows/ccpp.yml

@@ -21,6 +21,7 @@ jobs:
         path: 'fluxengine-testdata'
     - name: apt
       run: |
+        sudo apt update
         sudo apt install libudev-dev libsqlite3-dev protobuf-compiler libwxgtk3.2-dev libfmt-dev libprotobuf-dev libmagic-dev libmbedtls-dev libcurl4-openssl-dev libmagic-dev nlohmann-json3-dev libdbus-1-dev libglfw3-dev libmd4c-dev libfreetype-dev libcli11-dev libboost-regex-dev
     - name: make
       run: CXXFLAGS="-Wp,-D_GLIBCXX_ASSERTIONS" make -j`nproc` -C fluxengine