support/testing: test_check_package.py: fix flake8 line length error

Commit d631615eb1b8 (support/testing: test check-package ignore list) added
a too long line causing the check-flake8 target to fail:

support/testing/tests/utils/test_check_package.py:233:133:
E501 line too long (138 > 132 characters)

https://gitlab.com/buildroot.org/buildroot/-/jobs/3726245521

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

support/testing/tests/utils/test_check_package.py

@@ -230,5 +230,6 @@ class TestCheckPackage(unittest.TestCase):
         self.assert_warnings_generated_for_file(m)
         self.assertIn("{}:0: Indent was expected to fail, did you fixed the file and forgot to update .checkpackageignore_outdated?"
                       .format(subdir_file), w)
-        self.assertIn("{}:0: NewlineAtEof was expected to fail, did you fixed the file and forgot to update .checkpackageignore_outdated?"
+        self.assertIn("{}:0: NewlineAtEof was expected to fail, did you fixed the file and forgot to update "
+                      ".checkpackageignore_outdated?"
                       .format(subdir_file), w)