[migration/3.18] recover from bad CWSource.in_synchronization default value
The addition of this attribute in 3.13.8 had default=False, which made
no sense, and was fixed in 3.13.9. However no migration was done so
apps that ever saw the 3.13.8 code could still have '' as defaultval for
this attribute.
Disable security hooks for internal sessions
Fixes semantic change introduced in 96dba2efd16d where internal sessions
started to check attribute permissions.
Closes #3444095