[Compiler Bug]: Incorrect JS output when copying and updating global variable with `+=` in `useEffect`

### What kind of issue is this? - [x] React Compiler core (the JS output is incorrect, or your app works incorrectly after optimization) - [ ] babel-plugin-react-compiler (build issue installing or using the Babel plugin) - [ ] eslint-plugin-react-compiler (build issue installing or using the eslint plugin) - [ ] react-compiler-healthcheck (build issue installing or using the healthcheck script) ### Link to repro https://playground.react.dev/#N4Igzg9grgTgxgUxALhAGwQFwAQEtsC82ADANwA6AdlQgB4AOEMOAZlJXJrhJdgIL16ACgCU2YFWzYoYBAFEWLBJyGjCAPnGSp2ODzA4Y7AHJQAtgCMEMQnm1S9lSBgB0aCAHMhAcgSLlhuzeADTYRpSmltYi9njYANREAIwUvDowWLC8agSaEmk6uvoQru5e3nAYAIaUUPRhQaHhkVYwMQXYAL7anaEA2gC67VIZmFnYADwAJrgAbuoA8gDSEwD0M-NU3ZQgwSCOLLgeKCC4ZozM2JgAnvQI4tgACmhQHriUC-Rc+l3YLDAQMzYbwWKpWNAAWnoLzelAhGSqnAhenOuAwMHWuAM3lSVCE+Skq1WKPoaKq30oAFkIFMEMhsOQQFU0GhGVtsGByVjDggwE8Ye9PhSwCJSLtwAALCAAdwAkpRMNZKMywCgWCqEJ0gA ### Repro steps In a `useEffect`, when capturing a copy of a global variable, then incrementing the global variable with an AssignmentExpression (`i += 1`), React Compiler optimizes away the copied variable and instead changes to reference the global variable directly. 1. Create a component like: ```ts let i = 0; function App() { useEffect(() => { const runNumber = i; console.log("effect run", runNumber); i += 1; return () => { console.log("cleanup run", runNumber); }; }, []); return <div>OK</div>; } export function Main() { return <StrictMode><App /></StrictMode> } ``` Here we specifically capture a copy of `i` to `runNumber` before updating it for use in the cleanup function. 2. Expected output in `StrictMode`: ``` effect run 0 cleanup run 0 effect run 1 ``` 3. Observed output: ``` effect run 0 cleanup run 1 effect run 1 ``` 4. Check compiler output: ```js import { c as _c } from "react/compiler-runtime"; let i = 0; expo…