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GH-45578: [C++] Use max not min in MakeStatisticsArrayMaxApproximate test (#45579)



### Rationale for this change

The test was written for min instead of max.

### What changes are included in this PR?

Use max not min for MaxApproximate test case.

### Are these changes tested?

Yes, by dedicated unit tests.

### Are there any user-facing changes?
No
* GitHub Issue: #45578

Authored-by: arash andishgar <arashandishgar1@gmail.com>
Signed-off-by: Sutou Kouhei <kou@clear-code.com>