Revise markup to avoid unwanted checklist UI

.github/pull_request_template.md

@@ -17,31 +17,27 @@ Fixes #
 
 <!--
 
-If targeting the next patch release, use the appropriate x.y-backport
-label to enable the backport bot.
-
 In normal circumstances we only target changes at the upcoming minor
 release, or as a patch to the current minor version. If you need to
-port a security fix to an older release, highlight this here.
+port a security fix to an older release, highlight this here by listing
+all targeted releases.
+
+If targeting the next patch release, also add the relevant x.y-backport
+label to enable the backport bot.
 
 -->
 
-- [ ] 1.4.x
-- [ ] 1.3.x
+1.4.x
 
 ## Draft CHANGELOG entry
 
 <!--
 
-Choose a category:
+Choose a category, delete the others:
 
 -->
 
-- [ ] NEW FEATURES
-- [ ] UPGRADE NOTES
-- [ ] ENHANCEMENTS
-- [ ] BUG FIXES
-- [ ] EXPERIMENTS
+### NEW FEATURES | UPGRADE NOTES | ENHANCEMENTS | BUG FIXES | EXPERIMENTS
 
 <!--