fix(forward): deflake TestFailover (#7558)

In CI, the first two upstream attempts can stall on UDP and each
consume the default 2s read timeout. Possibly exhausting most of
the 5s forward deadline before the healthy third upstream is tried.
Lower the read timeout to make retries faster.

Signed-off-by: Ville Vesilehto <ville@vesilehto.fi>

plugin/forward/setup_test.go

@@ -7,6 +7,7 @@ import (
 	"reflect"
 	"strings"
 	"testing"
+	"time"
 
 	"github.com/coredns/caddy"
 	"github.com/coredns/coredns/core/dnsserver"
@@ -483,6 +484,12 @@ func TestFailover(t *testing.T) {
 		f.OnStartup()
 		defer f.OnShutdown()
 
+		// Reduce per-upstream read timeout to make the test fit within the
+		// per-query deadline defaultTimeout of 5 seconds.
+		for _, p := range f.proxies {
+			p.SetReadTimeout(500 * time.Millisecond)
+		}
+
 		m := new(dns.Msg)
 		m.SetQuestion("example.org.", dns.TypeA)
 		rec := dnstest.NewRecorder(&test.ResponseWriter{})