dashboard: add known issues for linux/loong64

(This will cause 'greplogs --triage' to filter out this builder by
default.)

Updates golang/go#53116.

Change-Id: Ib238c641b83f6aec3d1fd75933b7d8593313da21
Reviewed-on: https://go-review.googlesource.com/c/build/+/408938
Reviewed-by: Alex Rakoczy <alex@golang.org>
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>

dashboard/builders.go

@@ -2557,6 +2557,7 @@ func init() {
 			"GOARCH=loong64",
 			"GOHOSTARCH=loong64",
 		},
+		KnownIssues: []int{53116, 53093},
 	})
 	addBuilder(BuildConfig{
 		FlakyNet:       true,