Updated template gitignore with fastlane best practices (#33186)

Summary:
See https://docs.fastlane.tools/best-practices/source-control/

This commit reflects the best practices as outlined by fastlane.

## Changelog

[iOS] [Fixed] - Improved template fastlane gitignore

Pull Request resolved: #33186

Test Plan: no test plan

Reviewed By: cortinico

Differential Revision: D34518831

Pulled By: motiz88

fbshipit-source-id: eee1d332f24caa37bc48fd058bf0eb0e73f6bc1b

template/_gitignore

@@ -49,9 +49,10 @@ buck-out/
 # For more information about the recommended setup visit:
 # https://docs.fastlane.tools/best-practices/source-control/
 
-*/fastlane/report.xml
-*/fastlane/Preview.html
-*/fastlane/screenshots
+**/fastlane/report.xml
+**/fastlane/Preview.html
+**/fastlane/screenshots
+**/fastlane/test_output
 
 # Bundle artifact
 *.jsbundle