arrow

GH-36446: [C++] Minor style improvements in ConcatenateImpl (#36463)

### Rationale for this change

Fixing style in `ConcatenateImpl::ConcatenateImpl`

### What changes are included in this PR?

1. Remove `std::move` on a const-ref
2. Use a foreach loop

### Are these changes tested?

Yes, by existing tests.

### Are there any user-facing changes?

No.

* Closes: #36446

Authored-by: mwish <maplewish117@gmail.com>
Signed-off-by: Antoine Pitrou <antoine@python.org>