This makes the file permissions and shebangs conform to the linter added in the next commit.
- executable files must have a shebang
- files with a shebang must be executable
- Electrum ABC source files are generally not supposed to be executable, even if they have a `if __name__ == "__main__":` section (running individual test suites can still be done with `python -m electrumabc.tests.<filename>`)
Depends on D15432
Related to D15421