Add mypy checks to pull request workflow

https://github.com/yigbt/deepFPlearn/pull/12/commits/5a76438cc9ccf4c7ea9f887d0ec25cba89042f67
https://github.com/yigbt/deepFPlearn/pull/12/commits/e44617667af5ee358eadecf1ab72f638e0020dfa