scripts: pylib: fix twister report handling for junitparser >= 4.0.2

With junitparser 4.0.2, the JunitXml.fromfile() now returns a JUnitXml
instance. In order to access the junit.TestSuite instance, we must use
TestSuite.fromelem() to convert it back.

Signed-off-by: Daniel DeGrasse <ddegrasse@tenstorrent.com>

scripts/pylib/twister/twisterlib/harness.py

@@ -1124,7 +1124,8 @@ class Ctest(Harness):
             self.instance.reason = 'No tests collected'
             return
 
-        assert isinstance(suite, junit.TestSuite)
+        if not isinstance(suite, junit.TestSuite):
+            suite = junit.TestSuite.fromelem(suite)
 
         if suite.failures and suite.failures > 0:
             self.status = TwisterStatus.FAIL