Use fixes in PR template (#3886)

* Use `fixes` in PR template

* whatsnew

Author: max-sixty

.github/PULL_REQUEST_TEMPLATE.md

@@ -1,6 +1,6 @@
 <!-- Feel free to remove check-list items aren't relevant to your change -->
 
- - [ ] Closes #xxxx
+ - [ ] Fixes #xxxx
  - [ ] Tests added
  - [ ] Passes `isort -rc . && black . && mypy . && flake8`
  - [ ] Fully documented, including `whats-new.rst` for all changes and `api.rst` for new API

doc/whats-new.rst

@@ -36,6 +36,9 @@ Documentation
 
 Internal Changes
 ~~~~~~~~~~~~~~~~
+- Use ``Fixes`` rather than ``Closes`` in GitHub Pull Request template, allowing
+  linking to issues.
+  By `Maximilian Roos <https://github.com/max-sixty>`_
 
 
 .. _whats-new.0.15.1: