chore: re-enable array_union nested null array edge case test (#21773)

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- Closes #19798

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Upstream issue fixed, re-enable test

- apache/arrow-rs#9227

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Author: Jefffrey

datafusion/sqllogictest/test_files/array/array_union.slt

@@ -114,11 +114,10 @@ select array_union(arrow_cast([], 'LargeList(Int64)'), arrow_cast([], 'LargeList
 []
 
 # array_union scalar function #7
-# re-enable when https://github.com/apache/arrow-rs/issues/9227 is fixed
-# query ?
-# select array_union([[null]], []);
-# ----
-# [[]]
+query ?
+select array_union([[null]], []);
+----
+[[NULL]]
 
 query error DataFusion error: Error during planning: Failed to coerce arguments to satisfy a call to 'array_union' function:
 select array_union(arrow_cast([[null]], 'LargeList(List(Int64))'), arrow_cast([], 'LargeList(Int64)'));