Invoke python all via Python3_EXECUTABLE

[ye-luo]

Describe the bug

../CMake/compareGCOV.cmake:  execute_process(COMMAND python ${CTEST_SOURCE_DIRECTORY}/tests/coverage/compare_gcov.py --action merge --base-dir
../CMake/compareGCOV.cmake:  execute_process(COMMAND python ${CTEST_SOURCE_DIRECTORY}/tests/coverage/compare_gcov.py --action compare --base-dir
../CMake/run_pyscf.cmake:  add_pyscf_test(${BASE_NAME} python ${MY_WORKDIR} ${TEST_INPUT_PREFIX}.py)

../CMake/macros.cmake:            ${qmcpack_SOURCE_DIR}/tests/scripts/check_scalars.py
../CMake/test_labels.cmake:      COMMAND ${qmcpack_SOURCE_DIR}/tests/scripts/test_labels.py ${TEST_NAME} ${QMC_CUDA} ${QMC_COMPLEX}

There are more if I looked into tests folder.

Are there ways to stop running python via shebang so we can caught all places?

[PDoakORNL]

sed the shebang out, run everything, put them back?

[quantumsteve]

Which, if any, shebangs do we need to keep in the repository?

[jtkrogel]

Please keep all that are present in the nexus sub-directory. I don't want anyone to have to do python3 qmca ..., etc.