Pin stable/zed constraint in tox to release 33.0.0

We are going to release Tempest new tag 33.0.0 to declare
the end of support for stable/wallaby. stable/zed constraint
is latest stable constraints tested with current tempest hash
which is going to be used for 33.0.0 release.

Further information:
 https://docs.openstack.org/tempest/latest/requirement_upper_constraint_for_tempest.html

Change-Id: Ia8536e783df945a273b8697b128a5115104d3c12
diff --git a/tox.ini b/tox.ini
index 0b793f0..954bd35 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 @@
 allowlist_externals =
     find
 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