Lower minimum Node.js version to 20.19.4 (#52678)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/52678

From partner feedback, there's still appetite to support Node 20.x for the next <1y of life. Lower min version to `20.19.4` (Jul 2025) and widen test matrix in CI.

Changelog:
[General][Breaking] - Our new minimum Node version is Node.js 20 (Overrides #51840)

Reviewed By: cortinico

Differential Revision: D78494491

fbshipit-source-id: c8d9dc6250cb11f8a12ca7e761b65f4a8dae9265