- Fix missing format specifier in renderApplication invariant (#56329)

Summary:
The `invariant` call in `renderApplication` passes `rootTag` as a substitution argument, but the format string has no `%s` placeholder. When the invariant fails, the error message reads:

```
Expect to have a valid rootTag, instead got
```

instead of:

```
Expect to have a valid rootTag, instead got null
```

The value is silently dropped, making the error less useful for debugging.

## Changelog:

[General] [Fixed] - Fix missing format specifier in renderApplication invariant

Pull Request resolved: https://github.com/facebook/react-native/pull/56329

Test Plan:
- Verified with `invariant` directly: without `%s` the third argument is ignored, with `%s` it is substituted into the message.
- Prettier and ESLint checks pass.

Reviewed By: cipolleschi

Differential Revision: D104657367

Pulled By: javache

fbshipit-source-id: 6b0fad2371941207ef064fa7ea63cdf9aa61ae7f

packages/react-native/Libraries/ReactNative/renderApplication.js

@@ -47,7 +47,7 @@ export default function renderApplication<Props extends {...}>({
   displayMode,
   useOffscreen,
 }: RenderApplicationOptions<Props>) {
-  invariant(rootTag, 'Expect to have a valid rootTag, instead got ', rootTag);
+  invariant(rootTag, 'Expect to have a valid rootTag, instead got %s', rootTag);
 
   let renderable: React.MixedElement = (
     <AppContainer