Patch from the conan center index recipe

[MartinDelille]

Here are two patch that lives in the conan center index recipe.

Tell me if it is relevant of if it need some further improvements.

[firewave]

The changes look fine but somewhat arbitrary since the version-less Python shebang and CMAKE_SOURCE_DIR are still used all over the place. So some context what this is fixing specifically would be very helpful.

FYI #3812 has the shebang changes as a whole but unfortunately it appears it was abandoned by the author.

[MartinDelille]

I revert the python version related commit.

[MartinDelille]

I just rebase this PR against the main branch.

[firewave]

Thanks, but you still didn't explain what problem this is fixing.