Improve the error message

tmt/steps/report/junit.py

@@ -357,8 +357,8 @@ def _read_log_filter(log: Path) -> str:
         except etree.XMLSyntaxError as error:
             phase.verbose('rendered XML', xml_data, 'red')
             raise tmt.utils.ReportError(
-                'The generated XML output is not a valid XML file. Use `--verbose` argument '
-                'to show the output.') from error
+                'The generated XML output is not a valid XML file (SyntaxError). Use `--verbose` '
+                'argument to show the output.') from error
 
     # Do not be fooled by the `encoding` parameter: even with `utf-8`, `tostring()` will still
     # return bytes. `unicode`, on the other hand, would give us a string, but then, no XML