refactor: replace golang.org/x/exp/slices with slices (#16772)

The experimental functions in `golang.org/x/exp/slices` are now
available in the standard library since Go 1.21.

Reference: https://go.dev/doc/go1.21#slices

Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

coderd/workspacebuilds_test.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"net/http"
+	"slices"
 	"strconv"
 	"testing"
 	"time"
@@ -14,7 +15,6 @@ import (
 	"github.com/stretchr/testify/require"
 	"go.opentelemetry.io/otel"
 	"go.opentelemetry.io/otel/propagation"
-	"golang.org/x/exp/slices"
 	"golang.org/x/xerrors"
 
 	"cdr.dev/slog"