[Tempest Plugins] Tag stein-last

Stein branch is in Extended Maintenance now[1]. All Tempest
plugins are branchless which means master version of Tempest
and its plugins is used to test the supported stable branches.

Once stable branch is moved to EM state then, Tempest and its
plugins compatible tag needs to be released so that we can
keep testing the EM stable branches with this tag once master
Tempest and its plugins are not compatible[2].

This tag will help for testing the stable/stein with single
compatible tag of Tempest and its plugins.

Tagging 'stein-last' as well as a new version also with same hash.
Documenting this new tag name here
- https://review.opendev.org/c/openstack/project-team-guide/+/769821

More detail on compatible version policy for Tempest and its
plugins is here
- https://docs.openstack.org/tempest/latest/tempest_and_plugins_compatible_version_policy.html

[1] https://releases.openstack.org/stein/index.html
[2] https://docs.openstack.org/tempest/latest/stable_branch_support_policy.html

Change-Id: I89a88f9ef39ebeeeb32bde2ce928f9089fc6086d

deliverables/stein/mistral-tempest-plugin.yaml

@@ -13,3 +13,7 @@ releases:
       - hash: d724aaeafeefc0ae72206018932c3a2b9f7af66a
         repo: openstack/mistral-tempest-plugin
     version: 0.2.0
+  - version: stein-last
+    projects:
+      - repo: openstack/mistral-tempest-plugin
+        hash: 776b590bd6af2517238336a114a2b68332228fb2

deliverables/wallaby/mistral-tempest-plugin.yaml

@@ -9,3 +9,8 @@ repository-settings:
     tarball-base: mistral_tempest_tests
 team: mistral
 type: tempest-plugin
+releases:
+  - version: 1.2.0
+    projects:
+      - repo: openstack/mistral-tempest-plugin
+        hash: 776b590bd6af2517238336a114a2b68332228fb2