MINOR: [Docs][Python] Update python_test.cc reference (apache#44622)

### 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?

No.

Authored-by: Emmanuel Ferdman <emmanuelferdman@gmail.com>
Signed-off-by: Joris Van den Bossche <jorisvandenbossche@gmail.com>

docs/source/developers/python.rst

@@ -90,7 +90,7 @@ and look for the "custom options" section.
 .. note::
 
    There are a few low-level tests written directly in C++. These tests are
-   implemented in `pyarrow/src/python_test.cc <https://github.com/apache/arrow/blob/main/python/pyarrow/src/python_test.cc>`_,
+   implemented in `pyarrow/src/arrow/python/python_test.cc <https://github.com/apache/arrow/blob/main/python/pyarrow/src/arrow/python/python_test.cc>`_,
    but they are also wrapped in a ``pytest``-based
    `test module <https://github.com/apache/arrow/blob/main/python/pyarrow/tests/test_cpp_internals.py>`_
    run automatically as part of the PyArrow test suite.