dashboard: update ExpectNum for linux-loong64-3a5000

For golang/go#46229

Change-Id: Ie2896d28fc6c5e3f7e0544daccfd0c8e6e65bcf8
Reviewed-on: https://go-review.googlesource.com/c/build/+/407935
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Reviewed-by: Heschi Kreinick <heschi@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>

dashboard/builders.go

@@ -610,7 +610,7 @@ var Hosts = map[string]*HostConfig{
 		Notes:     "Loongson 3A5000 Box hosted by Loongson; loong64 is the short name of LoongArch 64 bit version",
 		Owners:    []*gophers.Person{gh("XiaodongLoong")},
 		IsReverse: true,
-		ExpectNum: 5,
+		ExpectNum: 3,
 		env: []string{
 			"GOROOT_BOOTSTRAP=/usr/lib/go-1.18",
 		},