dashboard: set known issue on freebsd-riscv64 builder

The port is not yet complete, and the builder hasn't started to pass.
Mark that on the dashboard with a known issue.

For golang/go#53466.

Change-Id: Ifaef69956ce64981bcaf95defd73b253cde67dfe
Reviewed-on: https://go-review.googlesource.com/c/build/+/435897
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Result: Gopher Robot <gobot@golang.org>
diff --git a/dashboard/builders.go b/dashboard/builders.go
index 1f47d3b..5a8f26f 100644
--- a/dashboard/builders.go
+++ b/dashboard/builders.go
@@ -2689,9 +2689,10 @@
 		HostType: "host-freebsd-arm64-dmgk",
 	})
 	addBuilder(BuildConfig{
-		Name:     "freebsd-riscv64-unmatched",
-		HostType: "host-freebsd-riscv64-unmatched",
-		env:      []string{"GO_TEST_TIMEOUT_SCALE=4"},
+		Name:        "freebsd-riscv64-unmatched",
+		HostType:    "host-freebsd-riscv64-unmatched",
+		env:         []string{"GO_TEST_TIMEOUT_SCALE=4"},
+		KnownIssues: []int{53466},
 	})
 	addBuilder(BuildConfig{
 		Name:           "plan9-arm",