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ARROW-15243: [CI][Python] Make PyArrow installation more robust in CI

On Debian/Ubuntu, the system-provided setuptools is patched to install into
the system-specific `dist-packages` directory.
However, the newer setuptools from upstream would install PyArrow in the wrong location (`site-packages`).

Therefore, use "pip install" instead of "python setup.py build" to get the right behaviour.

Closes #12069 from pitrou/ARROW-15243-py-install

Authored-by: Antoine Pitrou <antoine@python.org>
Signed-off-by: Krisztián Szűcs <szucs.krisztian@gmail.com>