Update TOX_CONSTRAINTS_FILE for stable/2025.2

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/2025.2 branch, tests will
continue to use the upper-constraints list on master.

Change-Id: I2d56a75436026bfc745714473bba7a9a4075ef2e
Signed-off-by: OpenStack Release Bot <infra-root@openstack.org>
Generated-By: openstack/project-config:roles/copy-release-tools-scripts/files/release-tools/functions

.gitreview

@@ -2,3 +2,4 @@
 host=review.opendev.org
 port=29418
 project=openstack/watcher.git
+defaultbranch=stable/2025.2

tox.ini

@@ -8,7 +8,7 @@ basepython = python3
 usedevelop = True
 allowlist_externals = find
                       rm
-install_command = pip install -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master} {opts} {packages}
+install_command = pip install -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/2025.2} {opts} {packages}
 setenv =
   VIRTUAL_ENV={envdir}
   OS_STDOUT_CAPTURE=1