Legacy renderToString should not support top level Suspense

Author: sebmarkbage

packages/react-dom-bindings/src/server/ReactFizzConfigDOMLegacy.js

@@ -172,7 +172,6 @@ export {
   completeResumableState,
   emitEarlyPreloads,
   supportsClientAPIs,
-  canHavePreamble,
   hoistPreambleState,
   isPreambleReady,
   isPreambleContext,
@@ -194,6 +193,10 @@ export function getViewTransitionFormatContext(
   return parentContext;
 }
 
+export function canHavePreamble(): boolean {
+  return false;
+}
+
 export function pushTextInstance(
   target: Array<Chunk | PrecomputedChunk>,
   text: string,

packages/react-dom/src/__tests__/ReactDOMServerPartialHydration-test.internal.js

@@ -2444,16 +2444,14 @@ describe('ReactDOMServerPartialHydration', () => {
 
     function App({showMore}) {
       return (
-        <div>
-          <SuspenseList revealOrder="together">
-            {a}
-            {showMore ? (
-              <Suspense fallback="Loading B">
-                <AlwaysSuspend />
-              </Suspense>
-            ) : null}
-          </SuspenseList>
-        </div>
+        <SuspenseList revealOrder="together">
+          {a}
+          {showMore ? (
+            <Suspense fallback="Loading B">
+              <AlwaysSuspend />
+            </Suspense>
+          ) : null}
+        </SuspenseList>
       );
     }