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GH-41371: [CI][Release] Use the latest Ruby on macOS (#41379)

### Rationale for this change

Ruby 2.7 doesn't exist on `macos-latest` (`macos-14`).

### What changes are included in this PR?

Use `ruby` as the Ruby version to use the latest Ruby.

### Are these changes tested?

Yes.

### Are there any user-facing changes?

No.
* GitHub Issue: #41371

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