Use stable constraint in tox to release new tag for Zed

We are going to release Tempest new tag to declare the start of
support for stable/zed. So that new tag use stable/zed
constraint in the tox env.

For example: if anyone use Tempest new tag (32.0.0) in future say
1 year later then tox env also should use the zed contstraint for
compatibility instead master.

These need to be move back to master constraint once release is done.

Change-Id: I188a23bf77855358535986256b17fcc4cc6405f9
diff --git a/tox.ini b/tox.ini
index 94eb4d9..4f055d7 100644
--- a/tox.ini
+++ b/tox.ini
@@ -12,7 +12,7 @@
     OS_TEST_PATH=./tempest/test_discover
     OS_TEST_TIMEOUT={env:OS_TEST_TIMEOUT:1200}
 deps =
-    -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+    -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/zed}
     -r{toxinidir}/requirements.txt
 
 [testenv]
@@ -29,7 +29,7 @@
 install_command = pip install {opts} {packages}
 allowlist_externals = *
 deps =
-    -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+    -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/zed}
     -r{toxinidir}/requirements.txt
     -r{toxinidir}/test-requirements.txt
 commands =
@@ -273,7 +273,7 @@
 
 [testenv:venv]
 deps =
-  -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+  -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/zed}
   -r{toxinidir}/requirements.txt
   -r{toxinidir}/doc/requirements.txt
 commands = {posargs}
@@ -288,7 +288,7 @@
 
 [testenv:docs]
 deps =
-  -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+  -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/zed}
   -r{toxinidir}/doc/requirements.txt
 commands =
   sphinx-apidoc -f -o doc/source/tests/compute tempest/api/compute
@@ -375,7 +375,7 @@
 
 [testenv:releasenotes]
 deps =
-  -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+  -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/zed}
   -r{toxinidir}/doc/requirements.txt
 commands =
   rm -rf releasenotes/build