cmd/coordinator: fix unformatted %s

This was accidentally left unformatted in CL 408696.

For golang/go#52653.

Change-Id: Ia47ef27e5f6a7b328f0b51b3378ef823ffcb03a9
Reviewed-on: https://go-review.googlesource.com/c/build/+/410242
Run-TryBot: Michael Pratt <mpratt@google.com>
Auto-Submit: Michael Pratt <mpratt@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
diff --git a/cmd/coordinator/coordinator.go b/cmd/coordinator/coordinator.go
index 4d881e1..2615d78 100644
--- a/cmd/coordinator/coordinator.go
+++ b/cmd/coordinator/coordinator.go
@@ -1502,7 +1502,7 @@
 	for _, b := range ts.slowBots {
 		if len(b.KnownIssues) > 0 {
 			issueBlock := new(strings.Builder)
-			issueBlock.WriteString("Note that builder %s has known issues:\n")
+			fmt.Fprintf(issueBlock, "Note that builder %s has known issues:\n", b.Name)
 			for _, i := range b.KnownIssues {
 				fmt.Fprintf(issueBlock, "\thttps://go.dev/issue/%d\n", i)
 			}