dashboard: add known issues for plan9-386, plan9-386-0intro, and plan9-amd64-0intro

For golang/go#52653.
Updates golang/go#29801.
Updates golang/go#49756.
Updates golang/go#50137.

Change-Id: Ided04da5c1e403c4a194c8c645c5179534a00907
Reviewed-on: https://go-review.googlesource.com/c/build/+/408698
TryBot-Result: Gopher Robot <[email protected]>
Run-TryBot: Bryan Mills <[email protected]>
Reviewed-by: Alex Rakoczy <[email protected]>
Auto-Submit: Bryan Mills <[email protected]>

Author: Bryan C. Mills

dashboard/builders.go

@@ -2204,7 +2204,8 @@ func init() {
 			}
 			return run
 		},
-		buildsRepo: plan9Default,
+		buildsRepo:  plan9Default,
+		KnownIssues: []int{29801},
 	})
 	addBuilder(BuildConfig{
 		Name:           "windows-amd64-2008",
@@ -2711,7 +2712,8 @@ func init() {
 			}
 			return run
 		},
-		buildsRepo: plan9Default,
+		buildsRepo:  plan9Default,
+		KnownIssues: []int{49756, 49327},
 	})
 	addBuilder(BuildConfig{
 		Name:     "plan9-386-0intro",
@@ -2725,7 +2727,8 @@ func init() {
 			}
 			return run
 		},
-		buildsRepo: plan9Default,
+		buildsRepo:  plan9Default,
+		KnownIssues: []int{50137, 50878},
 	})
 	addBuilder(BuildConfig{
 		Name:     "aix-ppc64",