[BUGFIX] Fix EmConfUtility::fixEmConf conflicts generation

EmConfUtility::fixEmConf generates a string instead
of an array for "$emConf['constraints']['conflicts']"

Resolves: #50628
Releases: 6.2, 6.1, 6.0
Change-Id: I37e026569e761b8550a9b0e6a1cb10835f6c899b
Reviewed-on: https://review.typo3.org/22892
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters