dashboard: add known issue for dragonfly-amd64

The cmd/go tests have been timing out frequently on this builder.
We are still investigating the root cause.

For golang/go#53577.

Change-Id: I841117e8c2cff7296869d7beedced364714b7cf9
Reviewed-on: https://go-review.googlesource.com/c/build/+/414614
Reviewed-by: David Chase <[email protected]>
Auto-Submit: Bryan Mills <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Bryan Mills <[email protected]>

Author: Bryan C. Mills

dashboard/builders.go

@@ -2790,6 +2790,7 @@ func init() {
 		distTestAdjust: noTestDirAndNoReboot,
 		env:            []string{"GO_TEST_TIMEOUT_SCALE=2"}, // see golang.org/issue/45216
 		SkipSnapshot:   true,
+		KnownIssues:    []int{53577},
 	})
 	addBuilder(BuildConfig{
 		Name:           "freebsd-arm-paulzhol",