[Python][Release] 12.0.1 has 12.0.0 metadata

### Describe the bug, including details regarding any error messages, version, and platform.

I'm trying to `pip3 install` pyarrow==12.0.1 from a requirements file and receive this:

```
WARNING: Requested pyarrow==12.0.1 from https://files.pythonhosted.org/packages/c5/68/d3410e975bebbf5be00c1238d0418345d8ec5d88b7a6c102211a1c967edd/pyarrow-12.0.1.tar.gz (from -r /tmp/requirements.txt (line 4)), but installing version 12.0.0
Discarding https://files.pythonhosted.org/packages/c5/68/d3410e975bebbf5be00c1238d0418345d8ec5d88b7a6c102211a1c967edd/pyarrow-12.0.1.tar.gz (from https://pypi.org/simple/pyarrow/) (requires-python:>=3.7): Requested pyarrow==12.0.1 from https://files.pythonhosted.org/packages/c5/68/d3410e975bebbf5be00c1238d0418345d8ec5d88b7a6c102211a1c967edd/pyarrow-12.0.1.tar.gz (from -r /tmp/requirements.txt (line 4)) has inconsistent version: expected '12.0.1', but metadata has '12.0.0'
ERROR: Could not find a version that satisfies the requirement pyarrow==12.0.1 (from versions: 0.9.0, 0.10.0, 0.11.0, 0.11.1, 0.12.0, 0.12.1, 0.13.0, 0.14.0, 0.15.1, 0.16.0, 0.17.0, 0.17.1, 1.0.0, 1.0.1, 2.0.0, 3.0.0, 4.0.0, 4.0.1, 5.0.0, 6.0.0, 6.0.1, 7.0.0, 8.0.0, 9.0.0, 10.0.0, 10.0.1, 11.0.0, 12.0.0, 12.0.1)
ERROR: No matching distribution found for pyarrow==12.0.1
```

Downloading the 12.0.1 tarball I see the string "12.0.0" as `default_version` in setup.py and also set in CMakeLists.txt.

### Component(s)

Packaging, Release

Inspect setup.py and CMakeLists.txt in the 12.0.1 source tarball, starting with the default_version values reported in the issue. Update the release metadata so it consistently identifies 12.0.1, then verify that installing the tarball reports version 12.0.1 rather than 12.0.0.

Written by the indexing model from the issue text.