Add as TODO

Author: MichaelChirico

inst/tests/mergelist.Rraw

@@ -68,4 +68,5 @@ local({
   test(13.03, ii, lapply(l, indices)) ## this tests that original indices have not been touched, shallow_duplicate in mergeIndexAttrib
 })
 test(13.04, cbindlist(list(data.table(a=1:2), data.table(b=3:4, key="b"))), data.table(a=1:2, b=3:4, key="b"))
+# TODO(#7116): this could be supported
 # test(13.05, cbindlist(list(data.table(a=1:2, key="a"), data.table(b=3:4, key="b"))), data.table(a=1:2, b=3:4, key=c("a", "b")))