Fix Fabric debug message when we set `fabric_enabled = false` in `rn-tester` (#32502)

Summary:
The debug message stays `Building RNTester with Fabric enabled.` even if we set `fabric_enabled = false`

This pull request changes the message like below when `fabric_enabled = false`

`Building RNTester with Fabric disabled.`

## Changelog

<!-- Help reviewers and the release process by writing your own changelog entry. For an example, see:
https://github.com/facebook/react-native/wiki/Changelog
-->

[iOS] [Fixed] - Fix the debug message for Fabric in rn-tester

Pull Request resolved: https://github.com/facebook/react-native/pull/32502

Reviewed By: sota000

Differential Revision: D32027858

Pulled By: lunaleaps

fbshipit-source-id: baf5301581e354f588830acd12a5e8171799b1ca