astropy vulnerable to RCE in TranformGraph().to_dot_graph function

Astropy is a project for astronomy in Python that fosters interoperability between Python astronomy packages. Version 5.3.2 of the Astropy core package is vulnerable to remote code execution due to improper input validation in the `TranformGraph().to_dot_graph` function. A malicious user can provide a command or a script file as a value to the `savelayout` argument, which will be placed as the first value in a list of arguments passed to `subprocess.Popen`. Although an error will be raised, the command or script will be executed successfully. Version 5.3.3 fixes this issue.