Add link to arrow-rs ticket in comments (#19479)

## Which issue does this PR close?

- Follow on to #19441

## Rationale for this change

In #19441 @Jefffrey filed a
follow on ticket for arrow-rs
apache/arrow-rs#9034

I wanted to leave the context of where it could be used in DataFusion so
we remember to use it when available

## What changes are included in this PR?

Add a comment with a reference to
apache/arrow-rs#9034

## Are these changes tested?

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## Are there any user-facing changes?
No, only comments

Author: alamb

datafusion/common/src/scalar/mod.rs

@@ -2989,6 +2989,8 @@ impl ScalarValue {
                 Some(value) => {
                     let mut builder =
                         StringViewBuilder::with_capacity(size).with_deduplicate_strings();
+                    // Replace with upstream arrow-rs code when available:
+                    // https://github.com/apache/arrow-rs/issues/9034
                     for _ in 0..size {
                         builder.append_value(value);
                     }