make check may throw KeyError while processing pytest's junitxml output

make check may end up with the following python error:

Traceback (most recent call last):
  File "/usr/home/ondrej/Projects/bind9/bin/tests/system/./convert-junit-to-trs.py", line 70, in <module>
    main()
  File "/usr/home/ondrej/Projects/bind9/bin/tests/system/./convert-junit-to-trs.py", line 66, in main
    sys.exit(junit_to_trs(junit_xml))
  File "/usr/home/ondrej/Projects/bind9/bin/tests/system/./convert-junit-to-trs.py", line 37, in junit_to_trs
    if node.attrib["type"] == "pytest.xfail":
KeyError: 'type'

Related #4262 (closed), #3810