github_mirror: update ssh secret name

The zuul post action seems to not be using the code it just merged, so a
new commit is necessary for the post action code to be used.

Similar to:
https://review.opendev.org/c/starlingx/update/+/879489

Change-Id: I8bd708a08678507f07737f6e3909a93898494682

Author: ader1990

.zuul.yaml

@@ -16,11 +16,11 @@
       git_mirror_repository: cloudbase/cloudbase-init
     secrets:
       - name: git_mirror_credentials
-        secret: cbsl-init-github-secret
+        secret: cbsl-init-github-secret-v2
         pass-to-parent: true
 
 - secret:
-    name: cbsl-init-github-secret
+    name: cbsl-init-github-secret-v2
     data:
       user: git
       host: github.com