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GH-44111: [CI][Python] Enable S3 tests on macOS CI (#44129)

### Rationale for this change

S3 support is enabled when building PyArrow for macOS (both on PR builds and in Crossbow wheel builds), but minio wan't installed before testing, therefore S3 support in PyArrow was not tested at all.

### What changes are included in this PR?

Ensure Minio is installed before running PyArrow tests on macOS builds.

### Are these changes tested?

Yes, by construction.

### Are there any user-facing changes?

No.

* GitHub Issue: #44111

Authored-by: Antoine Pitrou <antoine@python.org>
Signed-off-by: Antoine Pitrou <antoine@python.org>