RestrictedPython information leakage via `AttributeError.obj` and the `string` module

Impact

A user can gain access to protected (and potentially sensible) information indirectly via AttributeError.obj and the string module.

Patches

The problem will be fixed in version 7.3.

Workarounds

If the application does not require access to the module string, it can remove it from RestrictedPython.Utilities.utility_builtins or otherwise do not make it available in the restricted execution environment.