Update TOX_CONSTRAINTS_FILE for stable/2023.2

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/2023.2 branch, tests will
continue to use the upper-constraints list on master.

Change-Id: Ibe00f663e5369a495bc3efe3129ed311308e2f9d

Author: openstackadmin

tox.ini

@@ -54,7 +54,7 @@ commands =
 
 [testenv:docs]
 usedevelop = False
-deps = -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+deps = -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/2023.2}
        -r{toxinidir}/doc/requirements.txt
 commands=
     sphinx-build -W -b html doc/source doc/build/html -W
@@ -87,7 +87,7 @@ commands = bindep test
 
 [testenv:releasenotes]
 usedevelop = False
-deps = -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+deps = -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/2023.2}
        -r{toxinidir}/doc/requirements.txt
 commands = sphinx-build -a -W -E -d releasenotes/build/doctrees -b html releasenotes/source releasenotes/build/html