fix slice copy in 1.20 (#13389)

The slices package is added to the standard library in Go 1.21;
we need to import from the exp area to maintain compatibility with Go 1.20.

Signed-off-by: tyltr <tylitianrui@126.com>

model/histogram/generic_test.go

@@ -15,10 +15,10 @@ package histogram
 
 import (
 	"math"
-	"slices"
 	"testing"
 
 	"github.com/stretchr/testify/require"
+	"golang.org/x/exp/slices"
 )
 
 func TestGetBound(t *testing.T) {