Update pull request template checklist (#348)

Author: marandaneto

.github/pull_request_template.md

@@ -13,3 +13,4 @@
 - [ ] I added tests to verify the changes.
 - [ ] I updated the docs if needed.
 - [ ] No breaking change or entry added to the changelog.
+- [ ] If there are related changes in the [core](https://github.com/PostHog/posthog-android/tree/main/posthog) package, I've already released them, or I'll release them before this one.