quick-xml update breaks netdog XML serialization

[ginglis13]

What I expected to happen:

An instance built with latest changes to the core-kit can be connected to.

What actually happened:

The instance never reaches multi-user.target:

       Starting Generate network configuration...
[    6.103667] netdog[961]: Failed to write network interface configuration: Error serializing config for 'eth0' to XML: Unsupported operation: character `$` is not allowed at the start of an XML name `$unflatten=mode`
         Starting Disable kexec load syscalls...
         Starting Bottlerocket data store migrator...
[    6.299955] migrator[965]: 19:08:16 [INFO] Requested version 1.21.0 matches version of given datastore at '/var/lib/bottlerocket/datastore/v1.21.0_n6rIjKZJacoTzZab'; nothing to do
[  OK  ] Started ACPI event daemon.
[FAILED] Failed to start Generate network configuration.
See 'systemctl status generate-network-config.service' for details.

This appears to be due to Rust dependency updates in #34 , specifically to netdog's dependency quick-xml from 0.26.0 to 0.36.0. From the release notes for quick-xml 0.27.0, under Misc Changes:

#490: Removed $unflatten= special prefix for fields for serde (de)serializer, > because:
it is useless for deserializer
serializer was rewritten and does not require it anymore
This prefix allowed you to serialize struct field as an XML element and now
replaced by a more thoughtful system explicitly indicating that a field should
be serialized as an attribute by prepending @ character to its name

https://github.com/tafia/quick-xml/releases/tag/v0.27.0

How to reproduce the problem:

Build the core-kit and build an aws-k8s variant with the core-kit. Launch an instance with that variant, observe above logs in EC2 serial console