[goal] Migrate testing to ubuntu focal

As per victoria cycle testing runtime and community goal[1]
we need to migrate upstream CI/CD to Ubuntu Focal(20.04).

Fixing:
- bug#1886298
Bump the lower constraints for required deps which added python3.8 support
in their later version.

- add noqa for F811 error


Story: #2007865
Task: #40207

Closes-Bug: #1886298

[1] https://governance.openstack.org/tc/goals/selected/victoria/migrate-ci-cd-jobs-to-ubuntu-focal.h>

Change-Id: I700c395f63921bf03c80e67c149dd980d0848163

lower-constraints.txt

@@ -13,14 +13,14 @@ fixtures==3.0.0
 futurist==1.2.0
 gitdb==0.6.4
 GitPython==1.0.1
-greenlet==0.4.10
+greenlet==0.4.15
 iso8601==0.1.11
 Jinja2==2.10
 jsonschema==3.2.0
 keystoneauth1==3.4.0
 kombu==4.0.0
 linecache2==1.0.0
-MarkupSafe==1.0
+MarkupSafe==1.1.1
 mox3==0.20.0
 msgpack-python==0.4.0
 netaddr==0.7.18
@@ -49,7 +49,7 @@ python-dateutil==2.5.3
 python-mimeparse==1.6.0
 python-subunit==1.0.0
 pytz==2013.6
-PyYAML==3.12
+PyYAML==3.13
 repoze.lru==0.7
 requests==2.14.2
 requestsexceptions==1.2.0

oslo_versionedobjects/tests/test_objects.py

@@ -1923,7 +1923,7 @@ class TestObjectSerializer(_BaseTestCase):
             }
 
         @base.VersionedObjectRegistry.register  # noqa
-        class Parent(base.VersionedObject):
+        class Parent(base.VersionedObject):  # noqa
             VERSION = '1.1'
 
             fields = {