Update TOX_CONSTRAINTS_FILE for stable/2025.1

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/2025.1 branch, tests will
continue to use the upper-constraints list on master.

Change-Id: I22aecd09b1337e39e43837121882bd50f2a4bbca

Author: openstackadmin

tox.ini

@@ -102,7 +102,7 @@ usedevelop = False
 [testenv:docs]
 allowlist_externals =
   sphinx-build
-deps = -c{env:TOX_CONSTRAINTS_FILE:{toxinidir}/upper-constraints.txt}
+deps = -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/2025.1}
        -r{toxinidir}/doc/requirements.txt
 commands = sphinx-build -W -b html doc/source doc/build/html