codereview.cfg: dev.v2 branch

This tells the git-codereview utility to target the right upstream
branch when submitting changes.

Change-Id: I837d2e8fb73afd11a136d552a6aad0572ec480b7

codereview.cfg

@@ -1,3 +1,4 @@
 gerrit: https://forge.certus.one
 issuerepo: certusone/wormhole
-branch: main
+parent-branch: main
+branch: dev.v2