[dev.cmdgo] all: update codereview.cfg to specify branch info

Change-Id: Ifda23e964e380b9dd0343f37e01eb61308a6797c
Reviewed-on: https://go-review.googlesource.com/c/mod/+/345689
Trust: Michael Matloob <matloob@golang.org>
Run-TryBot: Michael Matloob <matloob@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>

codereview.cfg

diff --git a/codereview.cfg b/codereview.cfg
index 3f8b14b..8ae64ed 100644
--- a/codereview.cfg
+++ b/codereview.cfg
@@ -1 +1,3 @@
 issuerepo: golang/go
+branch: dev.cmdgo
+parent-branch: master