Fix typo in useSyncExternalStore main entry point error (#24631)

Author: francoischalifour

packages/use-sync-external-store/src/useSyncExternalStore.js

@@ -22,7 +22,7 @@ if (__DEV__) {
       'it only works with React 18+.' +
       '\n\n' +
       'If you wish to support React 16 and 17, import from ' +
-      "'use-sync-external-store/shim' instead. It will fall back to a shimmed" +
+      "'use-sync-external-store/shim' instead. It will fall back to a shimmed " +
       'implementation when the native one is not available.' +
       '\n\n' +
       "If you only support React 18+, you can import directly from 'react'.",