v13.0 Branch Preparation

Pins version of Flake8
Updates requirements to point to branch

Change-Id: I7bb2ae00d743fec3d6241da68b9f43be5311bb95
Signed-off-by: Mark Beierl <mark.beierl@canonical.com>
diff --git a/tox.ini b/tox.ini
index 3a5b32b..d6e8b71 100644
--- a/tox.ini
+++ b/tox.ini
@@ -53,7 +53,7 @@
 #######################################################################################
 [testenv:flake8]
 deps =
-        flake8
+        flake8==5.0.4
         flake8-import-order
 commands =
         flake8 osm_common/ setup.py