fix example/otel compile error (#2028)

[hidu]

1. fix compire error
2. fix example/* go.sum overdue error:

[del-keys-without-ttl]$ go run main.go

go: github.com/go-redis/redis/v8@v8.0.0-00010101000000-000000000000 requires
	github.com/onsi/gomega@v1.18.1: missing go.sum entry; to add it:
	go mod download github.com/onsi/gomega
go: github.com/go-redis/redis/v8@v8.0.0-00010101000000-000000000000 requires
	github.com/onsi/gomega@v1.18.1: missing go.sum entry; to add it:
	go mod download github.com/onsi/gomega

[vmihailenco]

Thanks