fix(template): reference App.tsx vs App.js in template text (#35377)

Summary:
The template has moved to typescript now, the self-reference needed an update

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[GENERAL] [FIXED] - reference App.tsx vs App.js in text of new typescript template

Pull Request resolved: #35377

Test Plan: It is just a text change - it either makes sense or it doesn't. I think it makes sense?

Reviewed By: cipolleschi

Differential Revision: D41386912

Pulled By: NickGerleman

fbshipit-source-id: 6e62c11567e8fbff70b123446a827b18af43e864

template/App.tsx

@@ -77,7 +77,7 @@ function App(): JSX.Element {
             backgroundColor: isDarkMode ? Colors.black : Colors.white,
           }}>
           <Section title="Step One">
-            Edit <Text style={styles.highlight}>App.js</Text> to change this
+            Edit <Text style={styles.highlight}>App.tsx</Text> to change this
             screen and then come back to see your edits.
           </Section>
           <Section title="See Your Changes">