dashboard: add darwin-amd64-longtest builder

Post-submit builds the same set as other "secondary" longtest builders,
like linux-386-longtest.

Trybot builds are not enabled for release branches due to lack of
capacity.

For golang/go#35678.

Change-Id: I60f15bfe8fe74072f35b20462cd9d13a111a1b31
Reviewed-on: https://go-review.googlesource.com/c/build/+/479837
Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Michael Pratt <mpratt@google.com>
Reviewed-by: Heschi Kreinick <heschi@google.com>
Run-TryBot: Michael Pratt <mpratt@google.com>

dashboard/builders.go

@@ -2627,6 +2627,23 @@ func init() {
 		distTestAdjust: noTestDirAndNoReboot,
 		env:            []string{"CGO_ENABLED=0"},
 	})
+	addBuilder(BuildConfig{
+		Name:     "darwin-amd64-longtest",
+		HostType: "host-darwin-amd64-13-aws",
+		Notes:    "macOS 13 with go test -short=false",
+		buildsRepo: func(repo, branch, goBranch string) bool {
+			b := buildRepoByDefault(repo)
+			if repo != "go" && !(branch == "master" && goBranch == "master") {
+				// For golang.org/x repos, don't test non-latest versions.
+				b = false
+			}
+			return b
+		},
+		needsGoProxy: true, // for cmd/go module tests
+		env: []string{
+			"GO_TEST_TIMEOUT_SCALE=5", // give them lots of time
+		},
+	})
 	addBuilder(BuildConfig{
 		Name:           "darwin-arm64-11",
 		HostType:       "host-darwin-arm64-11",

dashboard/builders_test.go

@@ -394,6 +394,8 @@ func TestTrybots(t *testing.T) {
 }
 
 func checkBuildersForProject(t *testing.T, gotBuilders []*BuildConfig, want []string) {
+	t.Helper()
+
 	var got []string
 	for _, bc := range gotBuilders {
 		got = append(got, bc.Name)