fix(cli): remove unnecessary PTY from TestServerCreateAdminUser/Validates (#25444)

Fixes https://linear.app/codercom/issue/PLAT-224

The Validates subtest only checks that `Run()` returns a validation
error and never reads PTY output. We don't need it in this test, so
removing.

> 🤖 Generated by Coder Agents

cli/server_createadminuser_test.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"database/sql"
 	"fmt"
+	"io"
 	"runtime"
 	"testing"
 
@@ -224,8 +225,7 @@ func TestServerCreateAdminUser(t *testing.T) {
 		}
 		connectionURL, err := dbtestutil.Open(t)
 		require.NoError(t, err)
-		ctx, cancelFunc := context.WithCancel(context.Background())
-		defer cancelFunc()
+		ctx := testutil.Context(t, testutil.WaitShort)
 
 		root, _ := clitest.New(t,
 			"server", "create-admin-user",
@@ -235,10 +235,7 @@ func TestServerCreateAdminUser(t *testing.T) {
 			"--email", "not-an-email",
 			"--password", "x",
 		)
-		pty := ptytest.New(t)
-		root.Stdout = pty.Output()
-		root.Stderr = pty.Output()
-
+		root.Stdout, root.Stderr = io.Discard, io.Discard
 		err = root.WithContext(ctx).Run()
 		require.Error(t, err)
 		require.ErrorContains(t, err, "'email' failed on the 'email' tag")