Bump Node.js to >=20.10.0

[ddbeck]

The version must 20.10.0 or later (as opposed to 20.0.0) because we need import attributes, which didn't land until the Node.js 18.19 and 20.10 release lines.

This fixes #2888.

[janbrasna]

With this bump the two import assertions (that would be blocking updates past v21.ish) could be replaced with with safely:

web-features/scripts/specs.ts

Line 3 in f7d00b7

import webSpecs from 'web-specs' assert { type: 'json' };

web-features/scripts/update-drafts.ts

Line 8 in f7d00b7

import webSpecs from "web-specs" assert { type: "json" };

[ddbeck]

Thanks for the suggestion, @janbrasna—I've fixed those.