Node.js 16.x is deprecated

Warning given when following Boost installation instructions:
```
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DEPRECATION WARNING

Node.js 16.x is no longer actively supported!

You will not receive security or critical stability updates for this version.

You should migrate to a supported version of Node.js as soon as possible.
Use the installation script that corresponds to the version of Node.js you
wish to install. e.g.

* https://deb.nodesource.com/setup_16.x — Node.js 16 "Gallium" (deprecated)
* https://deb.nodesource.com/setup_18.x — Node.js 18 "Hydrogen" (Maintenance)
* https://deb.nodesource.com/setup_19.x — Node.js 19 "Nineteen" (deprecated)
* https://deb.nodesource.com/setup_20.x — Node.js 20 LTS "Iron" (recommended)
* https://deb.nodesource.com/setup_21.x — Node.js 21 "Iron" (current)

Please see https://github.com/nodejs/Release for details about which
version may be appropriate for you.

The NodeSource Node.js distributions repository contains
information both about supported versions of Node.js and supported Linux
distributions. To learn more about usage, see the repository:
https://github.com/nodesource/distributions

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```