upstream ci: Rename CentOS 9 pipelines jobs to c9s.

The correct name for upcoming release of CentOS is CentOS 9 Stream,
usually abbreviated to 'c9s'. As we need to differentiate from the
stream and the standard versions, this patch modifies the Azure
piipelines to use 'c9s' instead of 'CentOS 9'.

molecule/c9s-build/molecule.yml

@@ -2,7 +2,7 @@
 driver:
   name: docker
 platforms:
-  - name: centos-9-build
+  - name: c9s-build
     image: "quay.io/centos/centos:stream9"
     dockerfile: Dockerfile
     hostname: ipaserver.test.local

molecule/c9s/molecule.yml

@@ -2,8 +2,8 @@
 driver:
   name: docker
 platforms:
-  - name: centos-9
-    image: quay.io/ansible-freeipa/upstream-tests:centos-9
+  - name: c9s
+    image: quay.io/ansible-freeipa/upstream-tests:c9s
     pre_build_image: true
     hostname: ipaserver.test.local
     dns_servers: