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GH-44428: [CI][C#] Use setup-python to use "pip install" (#44429)

### Rationale for this change

We can't use `pip install` with Ubuntu 24.04's Python.

### What changes are included in this PR?

Use `actions/setup-python` instead of Ubuntu 24.04's Python.

### Are these changes tested?

Yes.

### Are there any user-facing changes?

No.
* GitHub Issue: #44428

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