Merge branch '7.1' into 7.2

* 7.1:
  Remove subtree split checks
  Remove subtree split checks
  Revert "minor #54653 Auto-close PRs on subtree-splits (nicolas-grekas)"
  [SecurityBundle] Fix `container.build_hash` parameter binding
  [Serializer] Fix denormalizing a collection of union types
  [DoctrineBridge] Fix `UniqueEntityValidator` with proxy object

Author: fabpot

.gitattributes

@@ -1,4 +1,5 @@
 /Resources/bin/update_mime_types.php export-ignore
 /Tests export-ignore
 /phpunit.xml.dist export-ignore
-/.git* export-ignore
+/.gitattributes export-ignore
+/.gitignore export-ignore