cmd/gopherbot: disable "set vscode-go milestones" task

The maintner data model doesn't expose when an issue gets transferred
from one repo to another (that's golang.org/issue/37370), so GopherBot
currently doesn't skip transferred issues when processing them.

There turns out to be many transferred issues in the vscode-go repo,
causing gopherbot to take too many repetitive actions as reported in
golang.org/issue/45461. Skip the task by default until this is handled
better to avoid depleting the GitHub quota way too quickly.

For golang/go#45461.

Change-Id: I404c94b342f9a870f159d3cadef6cfa2a9979d2d
Reviewed-on: https://go-review.googlesource.com/c/build/+/308789
Trust: Dmitri Shuralyov <dmitshur@golang.org>
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Carlos Amedee <carlos@golang.org>

cmd/gopherbot/gopherbot.go

@@ -925,6 +925,13 @@ func (b *gopherbot) setMiscMilestones(ctx context.Context) error {
 }
 
 func (b *gopherbot) setVSCodeGoMilestones(ctx context.Context) error {
+	// Disabled in production for golang.org/issue/45461.
+	// Only run this task if it was explicitly requested
+	// via the --only-run flag.
+	if *onlyRun == "" {
+		return nil
+	}
+
 	vscode := b.corpus.GitHub().Repo("golang", "vscode-go")
 	if vscode == nil {
 		return nil