Update duckdb index files

.gitattributes

@@ -16,3 +16,4 @@ bicubic_x2/train/index.duckdb filter=lfs diff=lfs merge=lfs -text
 bicubic_x2/validation/index.duckdb filter=lfs diff=lfs merge=lfs -text
 realistic_wild_x4/train/index.duckdb filter=lfs diff=lfs merge=lfs -text
 realistic_wild_x4/validation/index.duckdb filter=lfs diff=lfs merge=lfs -text
+unknown_x3/train/index.duckdb filter=lfs diff=lfs merge=lfs -text

unknown_x3/train/index.duckdb

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:6ea1b7b8a1e3fd2bd000d3f827cd0604d7f5785c858e42ab03a8e69eb18abe7d
+size 1060864