[FOLLOWUP][CLEANUP] Streamline backend toolbar items

Add missing closing brace in ClearCacheToolbarItemSingle.html

Change-Id: Ic17e40a6dd0780ee71d446209033fc78b658f720
Resolves: #80554
Releases: master
Reviewed-on: https://review.typo3.org/52270


Reviewed-by: Frans Saris <franssaris@gmail.com>
Reviewed-by: Claus Due <claus@phpmind.net>
Tested-by: Claus Due <claus@phpmind.net>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Tested-by: Andreas Fernandez <typo3@scripting-base.de>