find Python3 in find_dependency

[m-fila]

BEGINRELEASENOTES

• find Python3 in find_dependency

ENDRELEASENOTES

Making find_dependecy for consistent with find_package. According to the docs find Python finds Python 3 or fallbacks to Python 2. find Python3 is just Python 3

Closes #912

[tmadlener]

We also need to change to Python3_EXECUTABLE here, I think:

podio/cmake/podioMacros.cmake

Line 158 in f99f12c

COMMAND ${Python_EXECUTABLE} ${podio_PYTHON_DIR}/podio_class_generator.py ${CLANG_FORMAT_ARG} ${SCHEMA_EVOLUTION_ARG} ${UPSTREAM_EDM_ARG} ${YAML_FILE} ${ARG_OUTPUT_FOLDER} ${datamodel} ${ARG_IO_BACKEND_HANDLERS} ${LANGUAGE_ARG} ${VERSION_ARG} ${OLD_DESCRIPTION_ARG}

Also this one should probably become a Python3_FIND_FRAMEWORK here:

podio/cmake/podioBuild.cmake

Line 186 in f99f12c

SET(Python_FIND_FRAMEWORK LAST)

[tmadlener]

EDM4hep is failing because there was an explicit mention of Python_EXECUTABLE as well which FindPython3 no longer populates. key4hep/EDM4hep#476 should make things such that EDM4hep builds with and without these changes.