Update PR checklist

Author: Ruinong Tian

.github/workflows/PR_TEMPLATE.md

@@ -1,5 +1,6 @@
 This pull request was created by GitHub Actions/AWS CodeBuild! Before merging, please do the following:
 - [ ] Review changelog/staleness report.
-- [ ] (Only for Minor/Major version releases) Review python package dependency and size report.
+- [ ] Review pinned_env.in files, when releasing Major/Minor version, try removing entries from there and build images.
+- [ ] Review python package dependency and size report.
 - [ ] Review build/test results by clicking *Build Logs* in CI Report (be patient, tests take ~4hr).
 - [ ] Review ECR Scan results.