Revert "[MINOR][TESTS] Use SparkContext.setLogLevel in QuietTest"

This reverts commit 9bab16a.

Author: HyukjinKwon

python/pyspark/testing/utils.py

@@ -194,16 +194,14 @@ def wrapper(*args: Any, **kwargs: Any) -> Any:
 
 class QuietTest:
     def __init__(self, sc):
-        self.sc = sc
+        self.log4j = sc._jvm.org.apache.log4j
 
     def __enter__(self):
-        self.old_level = (
-            self.sc._jvm.org.apache.log4j.LogManager.getRootLogger().getLevel().toString()
-        )
-        self.sc.setLogLevel("FATAL")
+        self.old_level = self.log4j.LogManager.getRootLogger().getLevel()
+        self.log4j.LogManager.getRootLogger().setLevel(self.log4j.Level.FATAL)
 
     def __exit__(self, exc_type, exc_val, exc_tb):
-        self.sc.setLogLevel(self.old_level)
+        self.log4j.LogManager.getRootLogger().setLevel(self.old_level)
 
 
 class PySparkTestCase(unittest.TestCase):