docs/process/branching-checklist: Fix a broken rune

cr-daily-branch ought to be called via cr-for-branches so that we take
the lock.  Otherwise strange things can occur if cron runs
cr-daily-branch in the same directory - in particular, it will be
likely to update the osstest revision, breaking everything.

Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>

docs/process/branching-checklist.txt

@@ -89,6 +89,6 @@ will take a while to take effect:
   ssh osstest.test-lab
   cd branches/for-xen-$v-testing.git
   screen -S $v
-  ./cr-daily-branch --real xen-$v-testing
+  BRANCHES=xen-$v-testing ./cr-for-branches branches -w "./cr-daily-branch --real"
 
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