Upgrade CI Node.js version from 16 to 20

[TaprootFreak]

Problem

CI currently uses Node.js v16.20.2, but many dependencies require Node 18+ or 20+:

Package	Required	CI Version
@playwright/test	>=18	v16.20.2
@ethereumjs/rlp	>=18	v16.20.2
@ethereumjs/tx	>=18	v16.20.2
@ethereumjs/util	>=18	v16.20.2
@metamask/providers	^18.18 | >=20	v16.20.2
@solana/accounts	>=20.18.0	v16.20.2
@solana/addresses	>=20.18.0	v16.20.2
@solana/codecs	>=20.18.0	v16.20.2
@noble/curves	>= 20.19.0	v16.20.2
@noble/hashes	>= 20.19.0	v16.20.2
commander	>=20	v16.20.2

These warnings appear in every CI run and may cause unexpected failures in the future.

Solution

Update the GitHub Actions workflow to use Node.js 20.x:

- name: Use Node.js 20.x
  uses: actions/setup-node@v3
  with:
    node-version: '20.x'

Additional Notes

• Node.js 16 reached End-of-Life in September 2023
• Node.js 20 is the current LTS version