Ensure people think about breaking changes and make breaking changes the default.

Author: m-mohr

.github/pull_request_template.md

@@ -8,6 +8,6 @@
 
 **PR Checklist:**
 
-- [ ] This PR has breaking changes.
+- [ ] This PR has **no** breaking changes.
 - [ ] I have added my changes to the [CHANGELOG](https://github.com/radiantearth/stac-spec/blob/dev/CHANGELOG.md) **or** a CHANGELOG entry is not required.
 - [ ] API only: I have run `npm run generate-all` to update the [generated OpenAPI files](https://github.com/radiantearth/stac-spec/blob/dev/api-spec/README.md#openapi-definitions).