Use full url instead to point to issue chooser

.github/pull_request_template.md

 # Please create an issue instead
 
-Hi there! Thanks for your input; however, we are not accepting pull requests at this time. If you have a suggestion or think you've found a bug, please create an [issue](issues/new/choose) instead.
+Hi there! Thanks for your input; however, we are not accepting pull requests at this time. If you have a suggestion or think you've found a bug, please create an [issue](https://github.com/Unity-Technologies/arfoundation-samples/issues/new/choose) instead.