dashboard: skip ios-amd64 SlowBot alias

It's known there is no builder for it yet.
Skip it so that TestSlowBotAliases passes.

For golang/go#42177.
Updates golang/go#42100.

Change-Id: I5f1a6b17e6aa4b57cbdea44f2eeb1d4817e5f67f
Reviewed-on: https://go-review.googlesource.com/c/build/+/264738
Trust: Dmitri Shuralyov <[email protected]>
Run-TryBot: Dmitri Shuralyov <[email protected]>
TryBot-Result: Go Bot <[email protected]>
Reviewed-by: Cherry Zhang <[email protected]>

Author: dmitshur

dashboard/builders.go

@@ -27,6 +27,7 @@ var slowBotAliases = map[string]string{
 	// Known missing builders:
 	"darwin-arm":   "", // TODO(golang.org/issue/37611): Remove once port is removed.
 	"darwin-arm64": "", // TODO(golang.org/issue/39782): Add builder for darwin/arm64.
+	"ios-amd64":    "", // There is no builder for the iOS Simulator. See issues 42100 and 42177.
 
 	"386":            "linux-386",
 	"aix":            "aix-ppc64",