Add support Node.js@21 in the CI

[UlisesGascon]

Main Changes

Add support for Node 21 in the CI (d4ecdb4) and appveyor (54ecfb7)

Note: Node 21.6.2 is last version available

Changelog

• d4ecdb4 build: support Node.js 21.x by @UlisesGascon
• 54ecfb7 build: support Node.js 21.x in appveyor by @UlisesGascon

[dougwilson]

LGTM. As soon as the patch gets released within the next couple days I'll make the minor branch and land this there per usual.