Node 18 has reached end-of-life on 2025-04-30 and is not supported

The `lza-validator` container throws the below at runtime:
```
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!! !!
!! Node 18 has reached end-of-life on 2025-04-30 and is not supported. !!
!! Please upgrade to a supported node version as soon as possible. !!
!! !!
!! This software is currently running on node v18.20.8. !!
!! As of the current release of this software, supported node releases are: !!
!! - ^22.0.0 (Planned end-of-life: 2027-04-30) !!
!! - ^20.0.0 (Planned end-of-life: 2026-04-30) !!
!! !!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
```
Ref: https://github.com/aws-samples/lza-validator/blob/main/Dockerfile#L1

Open Dockerfile at line 1, as referenced in the issue, and inspect the Node version used to build the lza-validator container. Update it to a supported release, then rebuild and run the container to confirm the Node end-of-life warning no longer appears.

Written by the indexing model from the issue text.