Update TOX_CONSTRAINTS_FILE for stable/victoria

Update the URL to the upper-constraints file to point to the redirect
rule on releases.openstack.org so that anyone working on this branch
will switch to the correct upper-constraints list automatically when
the requirements repository branches.

Until the requirements repository has as stable/victoria branch, tests will
continue to use the upper-constraints list on master.

Change-Id: I529786619c5daac94599bd2ff7636a131c95e97a

tox.ini

@@ -12,7 +12,7 @@ setenv = VIRTUAL_ENV={envdir}
          LANGUAGE=en_US:en
          LC_ALL=C
 deps =
-  -c{env:UPPER_CONSTRAINTS_FILE:https://opendev.org/openstack/requirements/raw/branch/master/upper-constraints.txt}
+  -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/victoria}
   -r{toxinidir}/requirements.txt
   -r{toxinidir}/test-requirements.txt
 usedevelop = True