[Stable/Unmaintained Only] Pin to last compatible tag for py3.8

Stable/2023.1 and Unmaintained xena/yoga/zed runs ubuntu-focal
jobs and since with [1] py3.8 pins are dropped from master
upper-constraints, so these branches can no longer use master
constraints with envs running with python3.8.
With this patch pinning tempest to the last compatible tag
for py3.8 i.e 41.0.0[2]

[1] https://review.opendev.org/c/openstack/requirements/+/925201
[2] https://lists.openstack.org/archives/list/openstack-discuss@\
    lists.openstack.org/thread/FOWV4UQZTH4DPDA67QDEROAESYU5Z3LE/

Depends-On: https://review.opendev.org/c/openstack/tempest/+/933716
Closes-Bug: #2085886
Change-Id: I5e714655ed329ea2c714f918e3dd843ca764c2c4

Author: karelyatin

stackrc

@@ -300,8 +300,8 @@ REQUIREMENTS_BRANCH=${REQUIREMENTS_BRANCH:-$TARGET_BRANCH}
 
 # Tempest test suite
 TEMPEST_REPO=${TEMPEST_REPO:-${GIT_BASE}/openstack/tempest.git}
-TEMPEST_BRANCH=${TEMPEST_BRANCH:-$BRANCHLESS_TARGET_BRANCH}
-TEMPEST_VENV_UPPER_CONSTRAINTS=${TEMPEST_VENV_UPPER_CONSTRAINTS:-master}
+TEMPEST_BRANCH=${TEMPEST_BRANCH:-41.0.0 }
+TEMPEST_VENV_UPPER_CONSTRAINTS=${TEMPEST_VENV_UPPER_CONSTRAINTS:-$REQUIREMENTS_DIR/upper-constraints.txt}
 
 
 ##############

tests/test_refs.sh

@@ -15,7 +15,7 @@
 
 echo "Ensuring we don't have crazy refs"
 
-REFS=`grep BRANCH stackrc | grep -v 'TARGET_BRANCH' | grep -v 'NOVNC_BRANCH'`
+REFS=`grep BRANCH stackrc | grep -v 'TARGET_BRANCH' | grep -v 'NOVNC_BRANCH' | grep -v 'TEMPEST_BRANCH'`
 rc=$?
 if [[ $rc -eq 0 ]]; then
     echo "Branch defaults must be one of the *TARGET_BRANCH values. Found:"