fix HashWithIndifferentAccess#to_hash behaviour
Fix HWIA#to_hash behavior with array of hashes.
Merge pull request #10784 from senny/10526_prevent_key_transformation

Prevent side effects in `Hash#with_indifferent_access`.
Conflicts:
	activesupport/CHANGELOG.md
Merge branch 'fix-hwia' into 4-0-0