Upgrade pylint version to 3.1.1 and fix pylint issues in that version

Change-Id: Ibf16dc9af6b528a3d3fef38bd038519fa65966e2
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>
diff --git a/tox.ini b/tox.ini
index 63aaf7a..607e58b 100644
--- a/tox.ini
+++ b/tox.ini
@@ -65,7 +65,7 @@
 deps =  {[testenv]deps}
         -r{toxinidir}/requirements-dev.txt
         -r{toxinidir}/requirements-test.txt
-        pylint==2.10.2
+        pylint==3.1.1
 commands =
     pylint -E n2vc