Update node Docker tag to v21 - autoclosed

This PR contains the following updates:

Package	Type	Update	Change
node	final	major	`12-alpine` -> `21-alpine`
node	stage	major	`12-alpine` -> `21-alpine`

nodejs/node (node)

### [`v21`](https://togithub.com/nodejs/node/blob/HEAD/CHANGELOG.md#2016-01-21-Version-426-Argon-LTS--TheAlphaNerd) Moved to doc/changelogs/CHANGELOG_V4.md#4.2.6. ### [`v20`](https://togithub.com/nodejs/node/blob/HEAD/CHANGELOG.md#2016-05-06-Version-01214-Maintenance--rvagg) Moved to doc/changelogs/CHANGELOG_V012.md#0.12.14. ### [`v19`](https://togithub.com/nodejs/node/blob/HEAD/CHANGELOG.md#2015-03-19-Version-160-chrisdickinson) Moved to doc/changelogs/CHANGELOG_IOJS.md#1.6.0. ### [`v18`](https://togithub.com/nodejs/node/blob/HEAD/CHANGELOG.md#2015-08-18-Version-310-Fishrock123) Moved to doc/changelogs/CHANGELOG_IOJS.md#3.1.0. ### [`v17`](https://togithub.com/nodejs/node/blob/HEAD/CHANGELOG.md#2015-11-17-Version-510-Stable--Fishrock123) Moved to doc/changelogs/CHANGELOG_V5.md#5.1.0. ### [`v16`](https://togithub.com/nodejs/node/blob/HEAD/CHANGELOG.md#2016-05-06-Version-01214-Maintenance--rvagg) Moved to doc/changelogs/CHANGELOG_V012.md#0.12.14. ### [`v15`](https://togithub.com/nodejs/node/blob/HEAD/CHANGELOG.md#2015-12-23-Version-424-Argon-LTS--jasnell) Moved to doc/changelogs/CHANGELOG_V4.md#4.2.4. ### [`v14`](https://togithub.com/nodejs/node/blob/HEAD/CHANGELOG.md#2016-05-06-Version-01214-Maintenance--rvagg) Moved to doc/changelogs/CHANGELOG_V012.md#0.12.14. ### [`v13`](https://togithub.com/nodejs/node/blob/HEAD/CHANGELOG.md#2016-03-31-Version-01213-LTS--rvagg) Moved to doc/changelogs/CHANGELOG_V012.md#0.12.13.

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Tim-Demo / JS-Demo