[goal] Migrate testing to ubuntu focal
[goal] Migrate testing to ubuntu focal

As per victoria cycle testing runtime and community goal[1]
we need to migrate upstream CI/CD to Ubuntu Focal(20.04).

Moving py38 job to focal.

Story: #2007865
Task: #40221

[1] https://governance.openstack.org/tc/goals/selected/victoria/migrate-ci-cd-jobs-to-ubuntu-focal.h>

Change-Id: I2a1ce0bda37a4764f7e56a9c15a283eefa46e17b

swiftstack/swift,tipabu/swift,openstack/swift,openstack/swift,openstack/swift,openstack/swift,swiftstack/swift,tipabu/swift,tipabu/swift,swiftstack/swift,tipabu/swift