by adding to each a python shebang and changing their file permissions from 644 to 755, as mentioned in #1734 (comment).
These files don't need to be executable in order to run gen_test_vectors.py and run_test_vectors.py but it is helpful to allow developers to invoke them directly.
Before:
$ ./reference.py
zsh: permission denied: ./reference.py
After:
$ ./reference.py
