[test] Add failing test for lambda turning value reactive

compiler/forget/src/__tests__/fixtures/compiler/_bug.lambda-mutated-non-reactive-to-reactive.expect.md

@@ -0,0 +1,43 @@
+
+## Input
+
+```javascript
+function f(a) {
+  let x;
+  (() => {
+    x = { a };
+  })();
+  return <div x={x} />;
+}
+
+```
+
+## Code
+
+```javascript
+import { unstable_useMemoCache as useMemoCache } from "react";
+function f(a) {
+  const $ = useMemoCache(3);
+  const c_0 = $[0] !== a;
+  let x;
+  if (c_0) {
+    (() => {
+      x = { a };
+    })();
+    $[0] = a;
+    $[1] = x;
+  } else {
+    x = $[1];
+  }
+  let t0;
+  if ($[2] === Symbol.for("react.memo_cache_sentinel")) {
+    t0 = <div x={x} />;
+    $[2] = t0;
+  } else {
+    t0 = $[2];
+  }
+  return t0;
+}
+
+```
+      

compiler/forget/src/__tests__/fixtures/compiler/_bug.lambda-mutated-non-reactive-to-reactive.js

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+function f(a) {
+  let x;
+  (() => {
+    x = { a };
+  })();
+  return <div x={x} />;
+}