GH-44622: [DOCS][Python] Update python_test.cc reference

[emmanuel-ferdman]

Rationale for this change

Commit 21dbf4a moved the location of python_test.cc.

What changes are included in this PR?

PR updates the reference to python_test.cc.

Are these changes tested?

Are there any user-facing changes?

• GitHub Issue: GH-44622: [DOCS][Python] Update python_test.cc reference #44622

[github-actions]

Thanks for opening a pull request!

If this is not a minor PR. Could you open an issue for this pull request on GitHub? https://github.com/apache/arrow/issues/new/choose

Opening GitHub issues ahead of time contributes to the Openness of the Apache Arrow project.

Then could you also rename the pull request title in the following format?

GH-${GITHUB_ISSUE_ID}: [${COMPONENT}] ${SUMMARY}

or

MINOR: [${COMPONENT}] ${SUMMARY}

In the case of PARQUET issues on JIRA the title also supports:

PARQUET-${JIRA_ISSUE_ID}: [${COMPONENT}] ${SUMMARY}

See also:

• Other pull requests
• Contribution Guidelines - Contributing Overview

[github-actions]

⚠️ GitHub issue #44622 has been automatically assigned in GitHub to PR creator.