XWIKI-11454: MergeUtils#mergeList forget to update modified state

(cherry picked from commit 65fd114dddf828344cff67a61ff0f46966d215bd)

Conflicts:
	xwiki-platform-core/xwiki-platform-oldcore/src/test/java/com/xpn/xwiki/internal/merge/MergeUtilsTest.java