cmd/gopherbot: print referenced repo in closeCherryPickIssues

Calls to addGitHubComment and closeGitHubIssue operate on ref.Repo.ID(),
so use it in printIssue call too, rather than hard-coding b.gorepo.ID().

There's no change in behavior now because the closeCherryPickIssues task
only closes issues in the main Go repository at this time, but it should
prevent confusion if that changes in the future.

For golang/go#39008.

Change-Id: Idb72eb884a917ce1eb4d9cc7fb6114e52ddee9db
Reviewed-on: https://go-review.googlesource.com/c/build/+/234023
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>
diff --git a/cmd/gopherbot/gopherbot.go b/cmd/gopherbot/gopherbot.go
index e1113df..74a79a3 100644
--- a/cmd/gopherbot/gopherbot.go
+++ b/cmd/gopherbot/gopherbot.go
@@ -1546,7 +1546,7 @@
 					// doesn't match the CL branch goX.Y version, so skip it.
 					continue
 				}
-				printIssue("close-cherry-pick", b.gorepo.ID(), gi)
+				printIssue("close-cherry-pick", ref.Repo.ID(), gi)
 				if err := b.addGitHubComment(ctx, ref.Repo, gi.Number, fmt.Sprintf(
 					"Closed by merging %s to %s.", cl.Commit.Hash, cl.Branch())); err != nil {
 					return err