[SPARK-24614][PYSPARK] Fix for SyntaxWarning on tests.py

## What changes were proposed in this pull request?
Fix for SyntaxWarning on tests.py

## How was this patch tested?
./dev/run-tests

Author: Rekha Joshi <[email protected]>

Closes apache#21604 from rekhajoshm/SPARK-24614.

Author: rekhajoshm

python/pyspark/sql/tests.py

@@ -1918,7 +1918,7 @@ def assert_invalid_writer(self, writer, msg=None):
                 self.fail("invalid writer %s did not fail the query" % str(writer))  # not expected
             except Exception as e:
                 if msg:
-                    assert(msg in str(e), "%s not in %s" % (msg, str(e)))
+                    assert msg in str(e), "%s not in %s" % (msg, str(e))
 
             finally:
                 self.stop_all()