Update PULL_REQUEST_TEMPLATE.md (#70105)
Summary:
Many users actually send things like `Fixes #{69696}` which then fails to properly close the corresponding issue.
Fixes #{issue number}
Pull Request resolved: https://github.com/pytorch/pytorch/pull/70105
Reviewed By: ejguan
Differential Revision: D33187501
Pulled By: albanD
fbshipit-source-id: 2080ee42c30b9db45177f049627118a6c3b544b7
