docs: deprecate bullseye (end of 5 year lifecycle on 2026-08-31)

[MikeMcC399]

Description

Add note to README > node:bullseye that Debian bullseye reaches the end of its 5-year lifecycle on Aug 31, 2026.

Motivation and Context

Users should plan to migrate before Debian bullseye is no longer supported.

A follow-on change after end of Aug 2026 will be needed to remove bullseye from the configuration and this documentation change advises users in advance.

Testing Details

N/A

Types of changes

• Documentation
• Version change (Update, remove or add more Node.js versions)
• Variant change (Update, remove or add more variants, or versions of variants)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Other (none of the above)

Checklist

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING.md document.
• All new and existing tests passed.

[MikeMcC399]

Preview

https://github.com/MikeMcC399/docker-node/tree/deprecate-bullseye#nodebullseye