all: use cibuild.On

Signed-off-by: Josh Bleecher Snyder <josh@tailscale.com>

ssh/tailssh/tailssh_test.go

@@ -26,6 +26,7 @@ import (
 	"tailscale.com/net/tsdial"
 	"tailscale.com/tailcfg"
 	"tailscale.com/types/logger"
+	"tailscale.com/util/cibuild"
 	"tailscale.com/util/lineread"
 	"tailscale.com/wgengine"
 )
@@ -245,9 +246,7 @@ func TestSSH(t *testing.T) {
 	}
 
 	t.Run("env", func(t *testing.T) {
-		if os.Getenv("CI") == "true" {
-			// CI env variable is set by GitHub.
-			// https://docs.github.com/en/actions/learn-github-actions/environment-variables#default-environment-variables
+		if cibuild.On() {
 			t.Skip("Skipping for now; see https://github.com/tailscale/tailscale/issues/4051")
 		}
 		cmd := execSSH("LANG=foo env")
@@ -292,9 +291,7 @@ func TestSSH(t *testing.T) {
 	})
 
 	t.Run("stdin", func(t *testing.T) {
-		if os.Getenv("CI") == "true" {
-			// CI env variable is set by GitHub.
-			// https://docs.github.com/en/actions/learn-github-actions/environment-variables#default-environment-variables
+		if cibuild.On() {
 			t.Skip("Skipping for now; see https://github.com/tailscale/tailscale/issues/4051")
 		}
 		cmd := execSSH("cat")

tstest/archtest/qemu_test.go

@@ -16,6 +16,8 @@ import (
 	"runtime"
 	"strings"
 	"testing"
+
+	"tailscale.com/util/cibuild"
 )
 
 func TestInQemu(t *testing.T) {
@@ -33,7 +35,7 @@ func TestInQemu(t *testing.T) {
 		{"mips64le", "mips64el"},
 		{"386", "386"},
 	}
-	inCI := os.Getenv("CI") == "true"
+	inCI := cibuild.On()
 	for _, arch := range arches {
 		arch := arch
 		t.Run(arch.Goarch, func(t *testing.T) {

util/cibuild/cibuild.go

@@ -9,5 +9,7 @@ import "os"
 
 // On reports whether the current binary is executing on a CI system.
 func On() bool {
-	return os.Getenv("GITHUB_ACTIONS") != ""
+	// CI env variable is set by GitHub.
+	// https://docs.github.com/en/actions/learn-github-actions/environment-variables#default-environment-variables
+	return os.Getenv("GITHUB_ACTIONS") != "" || os.Getenv("CI") == "true"
 }