upstream CI: Enable CentOS 8 Stream for PR and nightly tests.

Add configuration to build a testing CentOS 8 stream image and to
execute upstream tests using that image in pull requests (Ansible
2.9) and on the nightly tests (all supported Ansible versions).

tests/azure/azure-pipelines.yml

@@ -18,9 +18,9 @@ stages:
       scenario: fedora-latest
       ansible_version: ">=2.9,<2.10"
 
-# CentOS 9
+# CentOS 9 Stream
 
-- stage: CentOS9_Ansible_2_9
+- stage: c9s_Ansible_2_9
   dependsOn: []
   jobs:
   - template: templates/group_tests.yml
@@ -29,6 +29,17 @@ stages:
       scenario: centos-9
       ansible_version: ">=2.9,<2.10"
 
+# CentOS 8 Stream
+
+- stage: c8s_Ansible_2_9
+  dependsOn: []
+  jobs:
+  - template: templates/group_tests.yml
+    parameters:
+      build_number: $(Build.BuildNumber)
+      scenario: c8s
+      ansible_version: ">=2.9,<2.10"
+
 # CentOS 8
 
 - stage: CentOS8_Ansible_2_9