petals compatibility test fix pythonpath

Author: emanuel-schmid

script/jenkins/petals_regression_test/Jenkinsfile

@@ -14,7 +14,7 @@ pipeline {
         cp ~/jobs/petals_install_env/workspace/climada.conf climada.conf
         python script/jenkins/set_config.py test_directory ~/jobs/petals_install_env/workspace/climada_petals
 
-        pytest --junitxml=tests_xml/tests.xml ~/jobs/petals_install_env/workspace/climada_petals
+        PYTHONPATH=.:$PYTHONPATH pytest --junitxml=tests_xml/tests.xml ~/jobs/petals_install_env/workspace/climada_petals
 
         git checkout climada.conf
         '''