[SPARK-54948][PYTHON][TEST] Use the same testsuite name for same tests

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

Avoid the timestamp suffix on test suite name so codecov.io won't believe they are different tests.

### Why are the changes needed?

With different test suite names, the same test (with the same test name) will be considered different by codecov.io.

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

No

### How was this patch tested?

CI, but it should not have any real code impact

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

No

Closes #53715 from gaogaotiantian/testsuite-name.

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

Author: gaogaotiantian

python/pyspark/testing/unittestutils.py

@@ -22,7 +22,7 @@ def main(module="__main__", output="target/test-reports"):
     try:
         import xmlrunner
 
-        testRunner = xmlrunner.XMLTestRunner(output=output, verbosity=2)
+        testRunner = xmlrunner.XMLTestRunner(output=output, verbosity=2, outsuffix="")
     except ImportError:
         testRunner = None
     unittest.main(module=module, testRunner=testRunner, verbosity=2)