chore: Mention breaking changes in PR template (#8602)

Author: julian-risch

Diff for: .github/pull_request_template.md

@@ -20,6 +20,6 @@
 - I have read the [contributors guidelines](https://github.com/deepset-ai/haystack/blob/main/CONTRIBUTING.md) and the [code of conduct](https://github.com/deepset-ai/haystack/blob/main/code_of_conduct.txt)
 - I have updated the related issue with new insights and changes
 - I added unit tests and updated the docstrings
-- I've used one of the [conventional commit types](https://www.conventionalcommits.org/en/v1.0.0/) for my PR title: `fix:`, `feat:`, `build:`, `chore:`, `ci:`, `docs:`, `style:`, `refactor:`, `perf:`, `test:`.
+- I've used one of the [conventional commit types](https://www.conventionalcommits.org/en/v1.0.0/) for my PR title: `fix:`, `feat:`, `build:`, `chore:`, `ci:`, `docs:`, `style:`, `refactor:`, `perf:`, `test:` and added `!` in case the PR includes breaking changes.
 - I documented my code
 - I ran [pre-commit hooks](https://github.com/deepset-ai/haystack/blob/main/CONTRIBUTING.md#installation) and fixed any issue