add qsymm to the testing docker images

This fix will need to be backported to stable too, but we want the
testing images to be built on master, as other requirements
(specifically doc building) have changed.

docker/Dockerfile.debian

@@ -21,6 +21,10 @@ RUN echo "deb http://downloads.kwant-project.org/debian/ stable main" >> /etc/ap
     && apt-get clean && \
     rm -rf /var/lib/apt/lists/*
 
+### install optional dependencies not available from the Debian repositories
+RUN pip3 install \
+    qsymm==1.2.6
+
 ### install build and testing dependencies
 RUN pip3 install \
       cython \

docker/Dockerfile.ubuntu

@@ -19,6 +19,10 @@ RUN apt-add-repository -s ppa:kwant-project/ppa && \
     && apt-get clean && \
     rm -rf /var/lib/apt/lists/*
 
+### install optional dependencies not available from the Debian repositories
+RUN pip3 install \
+    qsymm==1.2.6
+
 ### install build and testing dependencies
 RUN pip3 install \
       cython \

docker/kwant-latest.yml

@@ -8,6 +8,7 @@ dependencies:
     - tinyarray
     - sympy
     - matplotlib
+    - qsymm
     # Linear algebra libraraies
     - mumps
     - blas #=1.1 openblas