Add test suite run check to the PR template (#44)

This ensures contributors run the test suite in their local
environments before submitting a PR and verify that their changes
introduce no new errors.

Author: pavelacamposp

.github/PULL_REQUEST_TEMPLATE.md

@@ -17,5 +17,6 @@ Closes # (issue)
 
 - [ ] I have run the [`pre-commit`](https://pre-commit.com/) checks either with `pre-commit run --all` or by integrating `pre-commit` into my workflow
 - [ ] I have added tests to ensure my changes work as expected without errors (if applicable)
+- [ ] I have run the test suite locally with `pytest` and verified that all tests pass
 - [ ] I have provided clear context, rationale, and linked any related issues (if applicable)
 - [ ] I have updated the documentation (if applicable)