docs(vex): use debian minor version in examples

[DmitriyLewen]

Description

To ensure the examples continue to work, we must use Debian images with a specific minor version (e.g. debian:11.8).

Checklist

• I've read the guidelines for contributing to this repository.
• I've followed the conventions in the PR title.
• I've added tests that prove my fix is effective or that my feature works.
• I've updated the documentation with the relevant information (if needed).
• I've added usage information (if the PR introduces new options)
• I've included a "before" and "after" example to the description (if the PR is a user interface change).