Update pull_request_template.md

.github/pull_request_template.md

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-(Please replace this header with a description of your pull request. Please include *BOTH* what you did and why you made the changes. The "why" may simply be citing a relevant Galaxy issue.)
-(If fixing a bug, please add any relevant error or traceback)
-(For UI components, it is recommended to include screenshots or screencasts)
-
-## How to test the changes?
-(Select all options that apply)
-- [ ] I've included appropriate [automated tests](https://docs.galaxyproject.org/en/latest/dev/writing_tests.html).
-- [ ] This is a refactoring of components with existing test coverage.
-- [ ] Instructions for manual testing are as follows:
-  1. [add testing steps and prerequisites here if you didn't write automated tests covering all your changes]
-
-## License
-- [x] I agree to license these and all my past contributions to the core galaxy codebase under the [MIT license](https://opensource.org/licenses/MIT).
+- [ ] Pull requests should be merged only after a parallel PR to [galaxyproject/galaxy](https://github.com/galaxyproject/galaxy) has been merged.
+- [ ] Please link to the above PR here