dashboard: mark all linux-loong64 builders as migrated to LUCI

All builders are now running on LUCI.

Updates golang/go#65398

Change-Id: If2b0703ba0b6defd90d89c42895345eea30fd8cf
Reviewed-on: https://go-review.googlesource.com/c/build/+/585175
Reviewed-by: Dmitri Shuralyov <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
Reviewed-by: Cherry Mui <[email protected]>
Auto-Submit: Dmitri Shuralyov <[email protected]>

Author: abner-chenc

dashboard/builders.go

@@ -2918,6 +2918,7 @@ var BuildersPortedToLUCI = map[string]bool{
 	"linux-ppc64le-power10osu": true, // Available as https://ci.chromium.org/p/golang/builders/ci/gotip-linux-ppc64le_power10.
 	"linux-ppc64-sid-buildlet": true, // Available as https://ci.chromium.org/p/golang/builders/ci/gotip-linux-ppc64_power8.
 	"linux-ppc64-sid-power10":  true, // Available as https://ci.chromium.org/p/golang/builders/ci/gotip-linux-ppc64_power10.
+	"linux-loong64-3a5000":     true, // Available as https://ci.chromium.org/p/golang/builders/ci/gotip-linux-loong64.
 
 	"netbsd-arm64-bsiegert": true, // Available as https://ci.chromium.org/p/golang/builders/ci/gotip-netbsd-arm64.