config validation fails when using !include tag

[ap-hyperbole]

When using !include tag in the netwrok-config.yaml file, and then running "yarn validate-config" I get parsing network-config failed unknown tag !<!include:> (5760:51) error

To Reproduce
In the networking-config.yaml add

vpcTemplates:
  - !include: ./network/vpc-templates/sandbox.yaml

network/vpc-templates/sandbox.yaml file contents

name: lz-sandbox-vpc
deploymentTargets:
  organizationalUnits:
    - Sandbox
region: {{ AcceleratorHomeRegion }}
cidrs:
  - {{ sandbox-vpc-cidr }}
enableDnsHostnames: true
enableDnsSupport: true
instanceTenancy: default
internetGateway: false
routeTables:
  - name: lz-sandbox-rt
    routes:
      # Only route to VPC endpoints
      - name: S3GatewayEndpoint
        type: gatewayEndpoint
        target: s3
subnets:
  - name: lz-sandbox-private-a
    availabilityZone: a
    routeTable: lz-sandbox-rt
    ipv4CidrBlock: {{ sandbox-vpc-private-subnet-a }}
  - name:lz-sandbox-private-b
    availabilityZone: b
    routeTable: lz-sandbox-rt
    ipv4CidrBlock: {{ sandbox-vpc-private-subnet-b }}
  - name: lz-sandbox-private-c
    availabilityZone: c
    routeTable: lz-sandbox-rt
    ipv4CidrBlock: {{ sandbox-vpc-private-subnet-c }}

Run yarn validate from landing-zone-accelerator-on-aws/source directory

yarn validate-config ../../aws-accelerator-config                                       
yarn run v1.22.22
$ ts-node ./packages/@aws-accelerator/accelerator/lib/config-validator.ts ../../aws-accelerator-config
2026-01-09 17:09:25.355 | info | config-validator | homeRegion set to 
2026-01-09 17:09:25.356 | info | config-validator | Found replacement variables in customizations-config.yaml
2026-01-09 17:09:25.356 | info | config-validator | Config source directory -  ../../aws-accelerator-config
2026-01-09 17:09:28.416 | error | network-config | parsing network-config failed unknown tag !<!include:> (5760:51)

 5757 |  ... 
 5758 |  ... andbox VPC ------------ #
 5759 |  ... 
 5760 |  ... rk/vpc-templates/sandbox.yaml
------------------------------------------^
 5761 |  ... 
 5762 |  ... 
2026-01-09 17:09:28.489 | info | accounts-config-validator | accounts-config.yaml file validation started
2026-01-09 17:09:28.490 | info | global-config-validator | global-config.yaml file validation started
2026-01-09 17:09:28.491 | info | global-config-validator | email count: 1
2026-01-09 17:09:28.491 | info | global-config-validator | email count: 1
2026-01-09 17:09:28.491 | info | global-config-validator | email count: 1
2026-01-09 17:09:28.491 | info | global-config-validator | email count: 1
2026-01-09 17:09:28.491 | info | global-config-validator | email count: 1
2026-01-09 17:09:28.491 | info | organization-config-validator | organization-config.yaml file validation started
2026-01-09 17:09:28.496 | info | security-config-validator | security-config.yaml file validation started
2026-01-09 17:09:28.501 | info | replacement-config-validator | replacements-config.yaml file validation started
2026-01-09 17:09:28.503 | warn | config-validator | Config file validation failed !!!
2026-01-09 17:09:28.504 | warn | config-validator | Error: Could not parse network configuration in network-config.yaml config file
error Command failed with exit code 1.
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.

Expected behavior
Expect the validator to at least accept the !include tag or even better to recursively validate all included files.

Please complete the following information about the solution:

• Version: v1.14.1