[syncschema] only add to the `synchronized` set if all possible updates have been done
Otherwise a simple sync_schema(syncprops=False) turns the subsequent
sync_schema() calls into a no-op.
Closes #6510918.
Document: cubicweb-doc
Title: CubicWeb documentation
Author: Logilab
Abstract: Some base documentation for CubicWeb users and developpers
Section: Apps/Programming
Format: HTML
Index: /usr/share/doc/cubicweb-documentation/index.html
Files: /usr/share/doc/cubicweb-documentation/*.html