fix: document can be null, not just undefined

[SimenB]

Summary

Jest sets document to null, not undefined (or delete which the test from #11677 does) when tearing down the env. https://github.com/facebook/jest/blob/95f49691d3472d8187640f1b703209b93c2bcecc/packages/jest-environment-jsdom/src/index.ts#L135-L136

How did you test this change?

At work we get

/workspace/node_modules/react-dom/cjs/react-dom.development.js:3905
      var evt = document.createEvent('Event');
                         ^
TypeError: Cannot read properties of null (reading 'createEvent')
    at Object.invokeGuardedCallbackDev (/workspace/node_modules/react-dom/cjs/react-dom.development.js:3905:26)
    at invokeGuardedCallback (/workspace/node_modules/react-dom/cjs/react-dom.development.js:4056:31)
    at flushPassiveEffectsImpl (/workspace/node_modules/react-dom/cjs/react-dom.development.js:23543:11)
    at unstable_runWithPriority (/workspace/node_modules/scheduler/cjs/scheduler.development.js:468:12)
    at runWithPriority$1 (/workspace/node_modules/react-dom/cjs/react-dom.development.js:11276:10)
    at flushPassiveEffects (/workspace/node_modules/react-dom/cjs/react-dom.development.js:23447:14)
    at Object.<anonymous>.flushWork (/workspace/node_modules/react-dom/cjs/react-dom-test-utils.development.js:992:10)
    at Immediate.<anonymous> (/workspace/node_modules/react-dom/cjs/react-dom-test-utils.development.js:1003:11)
    at processImmediate (node:internal/timers:464:21)
    at process.topLevelDomainCallback (node:domain:152:15)
    at process.callbackTrampoline (node:internal/async_hooks:128:24)

sometimes. I've been unable to track down where in our code we're missing a teardown (unfortunately the stack only points to react internals, no trace back to user code), but the error can be cleaner 🙂

[sizebot]

Comparing: 51c558a...addfc4c

Critical size changes

Includes critical production bundles, as well as any change greater than 2%:

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
oss-stable/react-dom/cjs/react-dom.production.min.js	=	129.55 kB	129.55 kB	=	41.43 kB	41.43 kB
oss-experimental/react-dom/cjs/react-dom.production.min.js	=	134.52 kB	134.52 kB	=	42.89 kB	42.89 kB
facebook-www/ReactDOM-prod.classic.js	=	423.36 kB	423.36 kB	=	78.05 kB	78.05 kB
facebook-www/ReactDOM-prod.modern.js	=	411.92 kB	411.92 kB	=	76.30 kB	76.30 kB
facebook-www/ReactDOMForked-prod.classic.js	=	423.36 kB	423.36 kB	=	78.06 kB	78.06 kB

Significant size changes

Includes any change greater than 0.2%:

(No significant changes)

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