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: I96d7d6853f7c8748d0a72f8999595a889f421596

tox.ini

@@ -11,7 +11,7 @@ setenv = VIRTUAL_ENV={envdir}
          PYTHONWARNINGS=default::DeprecationWarning
 usedevelop = True
 install_command =pip install {opts} {packages}
-deps = -c{env:UPPER_CONSTRAINTS_FILE:https://opendev.org/openstack/requirements/raw/branch/master/upper-constraints.txt}
+deps = -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/victoria}
        -r{toxinidir}/requirements.txt
        -r{toxinidir}/test-requirements.txt
 whitelist_externals =