Issue #3268174 by Wim Leers, nod_, catch, lauriii: Bug in CKE 4 → 5 upgrade...

Issue #3268174 by Wim Leers, nod_, catch, lauriii: Bug in CKE 4 → 5 upgrade path "format" does not always map to "heading", it could map to "codeBlock" too, or both, or neither

(cherry picked from commit 196b68e9)