fix missing dep

.gitlab-ci.yml

@@ -55,6 +55,7 @@ stages:
       - make -j $NUM_BUILD_CORES -l $NUM_CORES
       - ctest -LE $CTEST_EXCLUDE_LABELS -C $CMAKE_BUILD_TYPE --output-on-failure -j $NUM_CORES -T Test
    after_script:
+      - pip3 install lxml
       - python3 cmake/ctest2junit.py build > report.xml
    tags:
       - docker
@@ -1921,6 +1922,7 @@ coverage:
       - MSBuild.exe walberla.sln /property:Configuration=$BUILD_CONFIGURATION /verbosity:minimal /maxcpucount:4
       - ctest -LE $CTEST_EXCLUDE_LABELS -C $BUILD_CONFIGURATION --output-on-failure -j 4 -T Test
    after_script:
+      - pip3 install lxml
       - python3 cmake/ctest2junit.py build > report.xml
    variables:
       CMAKE_GENERATOR: "Visual Studio 15 2017 Win64"
@@ -2114,6 +2116,7 @@ msvc-14.2_mpionly:
       - python3 -m pytest --junitxml=report.xml pystencils_walberla lbmpy_walberla
       - cd ..
    after_script:
+      - pip3 install lxml
       - python3 cmake/ctest2junit.py build > report.xml
    tags:
       - mac