Update duckdb index files

.gitattributes

@@ -6,3 +6,4 @@ bicubic_x8/train/index.duckdb filter=lfs diff=lfs merge=lfs -text
 bicubic_x8/validation/index.duckdb filter=lfs diff=lfs merge=lfs -text
 realistic_difficult_x4/train/index.duckdb filter=lfs diff=lfs merge=lfs -text
 realistic_difficult_x4/validation/index.duckdb filter=lfs diff=lfs merge=lfs -text
+unknown_x2/train/index.duckdb filter=lfs diff=lfs merge=lfs -text

unknown_x2/train/index.duckdb

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:b479f21de1213ca97cb7057b77bcde5f5c8ea39f40481bd09bd4bcf55b92a741
+size 1060864