GH-43785: [Python][CI] Correct PARQUET_TEST_DATA path in wheel tests (#…

…43786)

### Rationale for this change

Starting with #41580, the pyarrow tests now also rely on a file in the parquet-testing submodule. And the path to that directory is controlled by `PARQUET_TEST_DATA`, which appears to be set wrongly in the wheel test scripts, causing all wheel builds to fail at the moment.
 
* GitHub Issue: #43785

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

ci/scripts/python_wheel_unix_test.sh

@@ -54,7 +54,7 @@ export PYARROW_TEST_S3=${ARROW_S3}
 export PYARROW_TEST_TENSORFLOW=ON
 
 export ARROW_TEST_DATA=${source_dir}/testing/data
-export PARQUET_TEST_DATA=${source_dir}/submodules/parquet-testing/data
+export PARQUET_TEST_DATA=${source_dir}/cpp/submodules/parquet-testing/data
 
 if [ "${INSTALL_PYARROW}" == "ON" ]; then
   # Install the built wheels

ci/scripts/python_wheel_windows_test.bat

@@ -35,7 +35,7 @@ set PYARROW_TEST_TENSORFLOW=ON
 @REM set PYARROW_TEST_PANDAS=ON
 
 set ARROW_TEST_DATA=C:\arrow\testing\data
-set PARQUET_TEST_DATA=C:\arrow\submodules\parquet-testing\data
+set PARQUET_TEST_DATA=C:\arrow\cpp\submodules\parquet-testing\data
 
 @REM Install testing dependencies
 pip install -r C:\arrow\python\requirements-wheel-test.txt || exit /B 1