Bump publish workflow Node version from 20 to 22

[dpletiko]

Problem

The publish workflow (.github/workflows/publish.yml) sets node-version: "20",
which fails when pnpm 11.1.1 is installed via corepack. The failed run shows:

warn: This version of pnpm requires at least Node.js v22.13. You are using v20.20.2.

TypeError [ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING]: A dynamic import callback was not specified.

Failed run: https://github.com/laravel/stream/actions/runs/26769674888

Fix

Bump node-version from "20" to "22" in publish.yml.

Verification

Reproduced locally:

• nvm use 20.20.2 + corepack + pnpm 11.1.1 → same warning + ERR_VM_DYNAMIC_IMPORT_CALLBACK_MISSING error on pnpm -v / pnpm install
• nvm use 22 + corepack + pnpm 11.1.1 → pnpm install, pnpm build, pnpm test, pnpm lint all pass with no errors/warnings

Note: tests.yml and coding-standards.yml don't pin a Node version at all, so this
also brings publish.yml in line with the rest of CI.