Use upper constraints in pep8 job

use the same dependencies in both unit and lint tests,
newer versions of dependencies may bring things like
new flake8 extensions (example - neutron-lib).

Change-Id: I324a74aa35620bb3a3549c0ee77b02c22c74dbcf
Signed-off-by: Pavlo Shchelokovskyy <shchelokovskyy@gmail.com>
(cherry picked from commit 58ee56c)

Author: pshchelo

tox.ini

@@ -29,6 +29,7 @@ commands =
 
 [testenv:pep8]
 deps =
+    -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/2025.1}
     hacking~=6.1.0 # Apache-2.0
     flake8-import-order~=0.18.0# LGPLv3
     bashate~=2.1.0 # Apache-2.0