## Summary
Update the CodeSandbox CI configuration to use Node 20 instead of Node
18, so that it matches the Node version specified in .nvmrc. This
ensures consistency between local development environments and CI
builds, reducing the risk of version-related build issues.
Closes#34328
## How did you test this change?
- Verified that .nvmrc specifies Node 20 and .codesandbox/ci.json is
updated accordingly.
- Locally switched to Node 20 using nvm use 20 and successfully ran
build scripts for all packages: `react`, `react-dom`,
`react-server-dom-webpack`, and `scheduler`.
- Confirmed there are no Node 20–specific build errors or warnings
locally.
- CI on the feature branch will now run with Node 20, and all builds are
expected to succeed.
* Clean up Scheduler forks
* Un-shadow variables
* Use timer globals directly, add a test for overrides
* Remove more window references
* Don't crash for undefined globals + tests
* Update lint config globals
* Fix test by using async act
* Add test fixture
* Delete test fixture
* Add CodeSandbox CI Config
* Add default sandbox to build
* Make build more efficient and add scheduler
* Force build
* Add scheduler image
* Add scheduler/tracing to the build
* Force another build
