github: fix PR template formatting

GitHub preserves the new lines from the template file, which makes
rendered template looks weird...

.github/pull_request_template.md

@@ -1,19 +1,14 @@
 # Description
 
-Please include a summary of the change. Please also include relevant
-motivation and context. See
-[contribution guidelines](https://github.com/oneapi-src/oneDNN/blob/master/CONTRIBUTING.md)
-for more details. If the change fixes an issue not documented in the project's
-Github issue tracker, please document all steps necessary to reproduce it.
+Please include a summary of the change. Please also include relevant motivation and context. See [contribution guidelines](https://github.com/oneapi-src/oneDNN/blob/master/CONTRIBUTING.md) for more details. If the change fixes an issue not documented in the project's Github issue tracker, please document all steps necessary to reproduce it.
 
 Fixes # (github issue)
 
 # Checklist
 
 ## All Submissions
 
-- [ ] Do all unit and benchdnn tests (`make test` and `make test_benchdnn_*`)
-      pass locally?
+- [ ] Do all unit and benchdnn tests (`make test` and `make test_benchdnn_*`) pass locally?
 - [ ] Have you formatted the code using clang-format?
 
 ## New features
@@ -24,5 +19,4 @@ Fixes # (github issue)
 ## Bug fixes
 
 - [ ] Have you added relevant regression tests?
-- [ ] Have you included information on how to reproduce the issue (either in a
-      github issue or in this PR)?
+- [ ] Have you included information on how to reproduce the issue (either in a github issue or in this PR)?