'Sync new' option for mirroring isn't correctly deserialised

To reproduce: Set up a mirroring config and tick the 'Sync new' checkbox before saving.

Expected: ScriptRunner creates a configuration representing the entire remote project, which is listed in the 'Projects' section of the config list.

Actual: ScriptRunner creates no such configuration.

This appears to happen because ScriptRunner serialises the value of this checkbox as a list, but later tries to deserialise it as a singular value.