dashboard/builders: upgrade non-specific Linux builders to Stretch

We have to update the non-versioned builders sometime, and now seems as
good as any.

This is just an easy first step, still need to figure out vmx and
whether to disable the stretch builders on master/1.20.

For golang/go#56414.

Change-Id: I7f1ce4faa9c6fa1595b7a0c3c72d451b1d18e5f4
Reviewed-on: https://go-review.googlesource.com/c/build/+/445616
Run-TryBot: Heschi Kreinick <[email protected]>
Reviewed-by: Bryan Mills <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>
Auto-Submit: Heschi Kreinick <[email protected]>
Reviewed-by: Carlos Amedee <[email protected]>

Author: heschi

dashboard/builders.go

@@ -1494,7 +1494,7 @@ func init() {
 		buildsRepo: func(repo, branch, goBranch string) bool {
 			return repo == "go" || repo == "crypto"
 		},
-		HostType: "host-linux-amd64-stretch",
+		HostType: "host-linux-amd64-bullseye",
 		env:      []string{"GOARCH=386", "GOHOSTARCH=386", "GO386=softfloat"},
 	})
 	addBuilder(BuildConfig{
@@ -1562,7 +1562,7 @@ func init() {
 		}
 		addBuilder(BuildConfig{
 			Name:     "misc-compile" + suffix,
-			HostType: "host-linux-amd64-stretch",
+			HostType: "host-linux-amd64-bullseye",
 			tryBot:   defaultTrySet(),
 			env: []string{
 				"GO_DISABLE_OUTBOUND_NETWORK=1",
@@ -1661,7 +1661,7 @@ func init() {
 	})
 	addBuilder(BuildConfig{
 		Name:     "linux-amd64-staticlockranking",
-		HostType: "host-linux-amd64-stretch",
+		HostType: "host-linux-amd64-bullseye",
 		Notes:    "builder with GOEXPERIMENT=staticlockranking, see go.dev/issue/37937",
 		buildsRepo: func(repo, branch, goBranch string) bool {
 			return repo == "go"