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GH-41696: [Python][Packaging] Bump MACOSX_DEPLOYMENT_TARGET to 12 instead of 11 (#43137)

### Rationale for this change

As shown on the associated issue there seems to be a problem with `MACOSX_DEPLOYMENT_TARGET` 11 on the wheels.

### What changes are included in this PR?

Update `MACOSX_DEPLOYMENT_TARGET` everywhere to the latest supported macOS version.

### Are these changes tested?

Via CI, even though the issue was not reproducible on CI.

### Are there any user-facing changes?

Yes, wheels won't be available for macOS 11 but those were crashing on the previous release.
* GitHub Issue: #41696

Authored-by: Raúl Cumplido <raulcumplido@gmail.com>
Signed-off-by: Raúl Cumplido <raulcumplido@gmail.com>