fix: errors.Join requires Go 1.20 or later (#3442)

Signed-off-by: Xiaolong Chen <fukua95@gmail.com>

Author: cxljs

sentinel.go

@@ -16,6 +16,7 @@ import (
 	"github.com/redis/go-redis/v9/internal"
 	"github.com/redis/go-redis/v9/internal/pool"
 	"github.com/redis/go-redis/v9/internal/rand"
+	"github.com/redis/go-redis/v9/internal/util"
 )
 
 //------------------------------------------------------------------------------
@@ -782,7 +783,20 @@ func (c *sentinelFailover) MasterAddr(ctx context.Context) (string, error) {
 	for err := range errCh {
 		errs = append(errs, err)
 	}
-	return "", fmt.Errorf("redis: all sentinels specified in configuration are unreachable: %w", errors.Join(errs...))
+	return "", fmt.Errorf("redis: all sentinels specified in configuration are unreachable: %s", joinErrors(errs))
+}
+
+func joinErrors(errs []error) string {
+	if len(errs) == 1 {
+		return errs[0].Error()
+	}
+
+	b := []byte(errs[0].Error())
+	for _, err := range errs[1:] {
+		b = append(b, '\n')
+		b = append(b, err.Error()...)
+	}
+	return util.BytesToString(b)
 }
 
 func (c *sentinelFailover) replicaAddrs(ctx context.Context, useDisconnected bool) ([]string, error) {