[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>

typo3/sysext/filelist/Classes/FileList.php

@@ -334,7 +334,7 @@ public function getTable()
             if ($v === '_CLIPBOARD_') {
                 $theData[$v] = $this->renderClipboardHeaderRow(!empty($iOut));
             } elseif ($v === '_REF_') {
-                $theData[$v] = htmlspecialchars($this->getLanguageService()->getLL('c_' . $v));
+                $theData[$v] = htmlspecialchars($this->getLanguageService()->sL('LLL:EXT:core/Resources/Private/Language/locallang_core.xlf:labels._REF_'));
             } else {
                 // Normal row
                 $theData[$v]  = $this->linkWrapSort($this->folderObject->getCombinedIdentifier(), $v);