[BUGFIX] Show _REF_ label in filelist table header

A regression introduced with #87879 removed the _REF_ label in the
header table row of the filelist module. This commit fixes this bug.

Resolves: #90387
Relates: #87879
Releases: master
Change-Id: I7c7289352d81b09576fce6b266fb6c7a11daeeb1
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/63265


Reviewed-by: Claus Due <claus@phpmind.net>
Reviewed-by: Guido Schmechel <guido.schmechel@brandung.de>
Reviewed-by: Björn Jacob <bjoern.jacob@tritum.de>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Guido Schmechel <guido.schmechel@brandung.de>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>