Add missing header file required by a dependency of breathe

docker/Dockerfile.test-env

@@ -71,15 +71,19 @@ ENV OPENBLAS_NUM_THREADS=1 \
     OPENBLAS_VERBOSE=0
 
 # Install dependencies available via apt-get.
-# - First set of packages are required to build and run FEniCS.
-# - Second set of packages are recommended and/or required to build
+# - First set of packages are required to build FEniCS dependencies.
+# - Second set of packages are required to build and run FEniCS.
+# - Third set of packages are recommended and/or required to build
 #   documentation or tests.
-# - Third set of packages are optional, but required to run gmsh
+# - Fourth set of packages are optional, but required to run gmsh
 #   pre-built binaries.
 RUN export DEBIAN_FRONTEND=noninteractive && \
     apt-get -qq update && \
     apt-get -yq --with-new-pkgs -o Dpkg::Options::="--force-confold" upgrade && \
     apt-get -y install \
+    portaudio19-dev && \
+    #
+    apt-get -y install \
     cmake \
     g++ \
     gfortran \