Replace git.openstack.org URLs with opendev.org URLs

Change-Id: If60f0bea94b5cf1009466c6371a4c8ee06e9c728
diff --git a/tox.ini b/tox.ini
index 9941e12..6f8cd38 100644
--- a/tox.ini
+++ b/tox.ini
@@ -14,7 +14,7 @@
 install_command =
   pip install {opts} {packages}
 deps =
-  -c{env:UPPER_CONSTRAINTS_FILE:https://git.openstack.org/cgit/openstack/requirements/plain/upper-constraints.txt}
+  -c{env:UPPER_CONSTRAINTS_FILE:https://opendev.org/openstack/requirements/raw/branch/master/upper-constraints.txt}
   -r{toxinidir}/test-requirements.txt
 commands = stestr run --slowest {posargs}