[LOCAL] Port react-native-codegen new .gitignore from main

This is to bring https://github.com/facebook/react-native/blob/c3ff336326302d7988bf7c187c9dcabed3bae10d/.gitignore#L107 to release branch

.gitignore

@@ -103,6 +103,7 @@ package-lock.json
 /React/FBReactNativeSpec/FBReactNativeSpec
 /packages/react-native-codegen/lib
 /ReactCommon/react/renderer/components/rncore/
+/packages/rn-tester/NativeModuleExample/ScreenshotManagerSpec*
 
 # Visual studio
 .vscode