GH-36537: [Python] Ensure dataset writer follows default Parquet version of 2.6

[jorisvandenbossche]

Rationale for this change

When bumping the default Parquet write version from 1.0 to 2.4 and then to 2.6, we forgot to also bump that default in the parquet.dataset writer (ParquetFileWriteOptions).

This PR bumps that directly from 1.0 to 2.6 to follow the default of the pyarrow.parquet module.

Follow-up on #36137

Are these changes tested?

Yes

Are there any user-facing changes?

Different default version can give different types in the parquet file.

• Closes: [Python] Writing Parquet with pyarrow.dataset still defaults to Parquet version 1.0 #36537

[github-actions]

⚠️ GitHub issue #36537 has been automatically assigned in GitHub to PR creator.

[jorisvandenbossche]

@github-actions crossbow submit -g integration

[github-actions]

Revision: ea69499

Submitted crossbow builds: ursacomputing/crossbow @ actions-87a2b14740

Task	Status
test-conda-python-3.10-hdfs-2.9.2
test-conda-python-3.10-hdfs-3.2.1
test-conda-python-3.10-pandas-latest
test-conda-python-3.10-pandas-nightly
test-conda-python-3.10-spark-master
test-conda-python-3.11-dask-latest
test-conda-python-3.11-dask-upstream_devel
test-conda-python-3.11-pandas-upstream_devel
test-conda-python-3.8-pandas-1.0
test-conda-python-3.8-spark-v3.1.2
test-conda-python-3.9-pandas-latest
test-conda-python-3.9-spark-v3.2.0

[conbench-apache-arrow]

Conbench analyzed the 6 benchmark runs on commit f8256bd6.

There was 1 benchmark result indicating a performance regression:

• Commit Run on arm64-m6g-linux-compute at 2023-07-07 16:03:36Z
  • params=num_cols:64/is_partial:1/real_time, source=cpp-micro, suite=arrow-ipc-read-write-benchmark

The full Conbench report has more details.