Update CodeSandbox CI to Node 20 to match .nvmrc

[iamsmruti]

Website or app

https://github.com/facebook/react

Repro steps

1. Check the repository’s .nvmrc file — it specifies Node 20.
2. Check .codesandbox/ci.json — it currently specifies Node 18.
3. This mismatch may cause builds in CodeSandbox CI to use an older Node version than intended.

How often does this bug happen?

Every time

DevTools package (automated)

No response

DevTools version (automated)

No response

Error message (automated)

No response

Error call stack (automated)

Error component stack (automated)

GitHub query string (automated)