Fix ReactNativeHost to have default UIManagerProvider as null (#41593)

Summary:
Pull Request resolved: #41593

Fixing fallback to `getJSIModule()` by defaulting `getUIManagerProvider()` correctly to null

Reviewed By: christophpurrer

Differential Revision: D51500901

fbshipit-source-id: 91b692e6c88d736970b652179e14bc524a411d0e

packages/react-native/ReactAndroid/src/main/java/com/facebook/react/ReactNativeHost.java

@@ -132,7 +132,7 @@ protected final Application getApplication() {
   }
 
   protected @Nullable UIManagerProvider getUIManagerProvider() {
-    return reactApplicationContext -> null;
+    return null;
   }
 
   /** Returns whether or not to treat it as normal if Activity is null. */