One final missed dependency for github actions.

Author: kpeeters

.github/workflows/ccpp.yml

@@ -14,7 +14,7 @@ jobs:
       with:
           python-version: 3.7
     - name: get dependencies
-      run:  sudo apt-get install git cmake python3-dev g++ libpcre3 libpcre3-dev libgmp3-dev libgtkmm-3.0-dev libboost-all-dev libgmp-dev libsqlite3-dev uuid-dev texlive-base && python3 --version && which python3 && python3 -m pip install sympy
+      run:  sudo apt-get install git cmake python3-dev g++ libpcre3 libpcre3-dev libgmp3-dev libgtkmm-3.0-dev libboost-all-dev libgmp-dev libsqlite3-dev uuid-dev texlive-base && python3 --version && which python3 && python3 -m pip install sympy gmpy2
     - name: configure
       run:  mkdir build && cd build && cmake -DENABLE_MATHEMATICA=OFF ..
     - name: make