untrack test reports generated by test libraries (reporters) (#35187)

Summary:
- Untrack Test Reports generated by test libraries (reporters E.g. `jest-junit`)
- E.g. `/reports/junit/js-test-results.xml` report is generated; when we exec `yarn test-ci`, which is **_shouldn't_ be tracked**

### NOTE: Used `[skip ci]` to avoid wastage of compute resources �🌏
- Feel free to init tests manually if you find it necessary

## Changelog

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[GENERAL] [CHANGED] - Untrack Test Reports generated by test libraries (reporters E.g. `jest-junit`)

Pull Request resolved: https://github.com/facebook/react-native/pull/35187

Test Plan:
`yarn test-ci`
![image](https://user-images.githubusercontent.com/55224033/199709131-240d844c-a98a-419b-a370-cafe8e927de4.png)

Reviewed By: cipolleschi

Differential Revision: D40993282

Pulled By: sshic

fbshipit-source-id: 3fe150d3e8bd45cec56b50f2dc071002412e475e

.gitignore

@@ -82,6 +82,9 @@ package-lock.json
 /coverage
 /third-party
 
+# Test Reports
+/reports
+
 # Root dir shouldn't have Xcode project
 /*.xcodeproj