requirements-compliance: restrict junitparser version < 2

junitparser version 2 is incompatible with check_compliance.py, it fails
like this:

File "./scripts/ci/check_compliance.py", line 295, in parse_kconfig
   self.skip("Not a Zephyr tree (ZEPHYR_BASE unset)")
File "./scripts/ci/check_compliance.py", line 141, in skip
   self.case.result = Skipped(msg, "skipped")
File "/usr/local/lib/python3.9/site-packages/junitparser/junitparser.py"
   line 682, in result
   for entry in value:

TypeError: 'Skipped' object is not iterable

Signed-off-by: Marc Herbert <marc.herbert@intel.com>