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GH-43992: [C++] Add missing std::move() in array_nested.cc (#43993)



### Rationale for this change

Minor code enhancement in array_nested.cc

### What changes are included in this PR?

Use std::move for nested types

### Are these changes tested?

Covered by existing

### Are there any user-facing changes?

no

* GitHub Issue: #43992

Authored-by: mwish <maplewish117@gmail.com>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>