Move `flutter-devicelab-mac-45` to try pool

### Is there an existing issue for this?

- [X] I have searched the [existing infra issues](https://github.com/flutter/flutter/issues?q=is%3Aopen+is%3Aissue+label%3Ateam-infra)

### Type of Request

infra task

### Infrastructure Environment

LUCI

### What is happening?

N/A

### Steps to reproduce

N/A

### Expected results

N/A