better reference to python

[gonuke]

Description

Instead of relying on python being on the path with exactly that name, refer to $PYTHON_EXECUTABLE in CMakeLists.txt files.

Motivation and Context

PyNE runs python during CMake to generate the pyne_version.h file that is included in all C++. This is done with a CMake execute_process where the COMMAND has historically been specified as python. Not all systems have a python executable with that name; many are now only python3. Our CI always generates a python executable so we don't see this result.

Fixes #1530

Changes

Change the remaining reference to a bare python executable to the $PYTHON_EXECUTABLE discovered in the top level CMake process.

[gonuke]

I expanded this PR to fix some other CI issues

[bquan0]

lgtm, @gonuke. I like all the changes to the CI files to match the new build process.

[gonuke]

Go ahead and merge @bquan0 - when you think it's ready. The docker_publish workflow won't pass but I decided to skip reissuing this PR from a local branch. Let me know if you want me to do that.