tox: bump the pinned flake8 and pylint version (#1029)

tox: bump the pinned flake8 and pylint version

* pylint: fix W1406 (redundant-u-string-prefix)

The u prefix for strings is no longer necessary in Python >=3.0.

* pylint: disable W1514 (unspecified-encoding)
    
From https://www.python.org/dev/peps/pep-0597/ (Python 3.10):
    
The new warning stems form https://www.python.org/dev/peps/pep-0597,
which says:
    
  Developers using macOS or Linux may forget that the default encoding
  is not always UTF-8. [...] Even Python experts may assume that the
  default encoding is UTF-8. This creates bugs that only happen on Windows.
    
The warning could be fixed by always specifying encoding='utf-8',
however we should be careful to not break environments which are not
utf-8 (or explicitly state that only utf-8 is supported). Let's silence
the warning for now.

* _quick_read_instance_id: cover the case where load_yaml() returns None

Spotted by pylint:
 - E1135 (unsupported-membership-test)
 - E1136 (unsubscriptable-object)

LP: #1944414

1 files changed, 1 insertions, 1 deletions

diff --git a/tests/unittests/test_util.py b/tests/unittests/test_util.py
index 2290cab7..bc30c90b 100644
--- a/tests/unittests/test_util.py
+++ b/tests/unittests/test_util.py
@@ -604,7 +604,7 @@ class TestMultiLog(helpers.FilesystemMockingTestCase):
 class TestMessageFromString(helpers.TestCase):
 
     def test_unicode_not_messed_up(self):
-        roundtripped = util.message_from_string(u'\n').as_string()
+        roundtripped = util.message_from_string('\n').as_string()
         self.assertNotIn('\x00', roundtripped)