message: fix: ignore status message from output of mypy stubs check
  Newer versions of `mypy` included an additional message in the stubs
  output, e.g. `Found 5 error: ...` which breaks the parsing of the output
  when all of the test failures are being skipped.
diff: @@ -18,7 +18,7 @@ def test_stubs():
  '--mypy-config-file', MYPY_INI_PATH,
  ], stdout=subprocess.PIPE)
  if (stubs.returncode != 0):
  - errors = stubs.stdout.decode('utf-8').split('error')
  + errors = stubs.stdout.decode('utf-8').split('Found')[0].split('error')
  broken_stubs = []
  for error in errors:
  add_error = True
  