[SPARK-51739][PYTHON][FOLLOW-UP] Set spark.sql.execution.arrow.pyspark.validateSchema.enabled for 3.5 connect client build

### What changes were proposed in this pull request?

We have a scheduled build to test Spark 3.5 client with Spark 4.0 server but this fails. We should set the legacy conf to make the tests passing.

### Why are the changes needed?

Build fails as below (https://github.com/apache/spark/actions/runs/14502535136/job/40685331457):

```
======================================================================
ERROR [0.289s]: test_empty_rows (pyspark.sql.tests.connect.test_parity_arrow_map.ArrowMapParityTests.test_empty_rows)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/runner/work/spark/spark-3.5/python/pyspark/sql/tests/test_arrow_map.py", line 128, in test_empty_rows
    self.assertEqual(self.spark.range(10).mapInArrow(empty_rows, "a int").count(), 0)
                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/runner/work/spark/spark-3.5/python/pyspark/sql/connect/dataframe.py", line 248, in count
    pdd = self.agg(_invoke_function("count", lit(1))).toPandas()
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/runner/work/spark/spark-3.5/python/pyspark/sql/connect/dataframe.py", line 1663, in toPandas
    return self._session.client.to_pandas(query)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/runner/work/spark/spark-3.5/python/pyspark/sql/connect/client/core.py", line 873, in to_pandas
    table, schema, metrics, observed_metrics, _ = self._execute_and_fetch(
                                                  ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/runner/work/spark/spark-3.5/python/pyspark/sql/connect/client/core.py", line 1283, in _execute_and_fetch
    for response in self._execute_and_fetch_as_iterator(req):
  File "/home/runner/work/spark/spark-3.5/python/pyspark/sql/connect/client/core.py", line 1264, in _execute_and_fetch_as_iterator
    self._handle_error(error)
  File "/home/runner/work/spark/spark-3.5/python/pyspark/sql/connect/client/core.py", line 1503, in _handle_error
    self._handle_rpc_error(error)
  File "/home/runner/work/spark/spark-3.5/python/pyspark/sql/connect/client/core.py", line [153](https://github.com/apache/spark/actions/runs/14502535136/job/40685331457#step:10:154)9, in _handle_rpc_error
    raise convert_exception(info, status.message) from None
pyspark.errors.exceptions.connect.SparkConnectGrpcException: (org.apache.spark.SparkException) [ARROW_TYPE_MISMATCH] Invalid schema from SQL_MAP_ARROW_ITER_UDF: expected StructType(StructField(a,IntegerType,true)), got StructType(StructField(a,DoubleType,true)). SQLSTATE: 42K0G
```

### Does this PR introduce _any_ user-facing change?

No, test-only.

### How was this patch tested?

Will monitor the build.

### Was this patch authored or co-authored using generative AI tooling?

No.

Closes #50613 from HyukjinKwon/SPARK-51739-followup.

Authored-by: Hyukjin Kwon <[email protected]>
Signed-off-by: Hyukjin Kwon <[email protected]>

Author: HyukjinKwon

.github/workflows/build_python_connect35.yml

@@ -90,7 +90,8 @@ jobs:
           # Start a Spark Connect server for local
           PYTHONPATH="python/lib/pyspark.zip:python/lib/py4j-0.10.9.9-src.zip:$PYTHONPATH" ./sbin/start-connect-server.sh \
             --driver-java-options "-Dlog4j.configurationFile=file:$GITHUB_WORKSPACE/conf/log4j2.properties" \
-            --jars "`find connector/protobuf/target -name spark-protobuf-*SNAPSHOT.jar`,`find connector/avro/target -name spark-avro*SNAPSHOT.jar`"
+            --jars "`find connector/protobuf/target -name spark-protobuf-*SNAPSHOT.jar`,`find connector/avro/target -name spark-avro*SNAPSHOT.jar`" \
+            --conf spark.sql.execution.arrow.pyspark.validateSchema.enabled=false
 
           # Checkout to branch-3.5 to use the tests in branch-3.5.
           cd ..