[migration] More resilient migration script Query the information schema to retrieve existing constraint (primary key and unique) and drop them. Thus don't use anymore DROP CONSTRAINT IF EXISTS (not implemented by e.g. old versions of sqlserver). To do so a missing DISTINCT was necessary to avoid duplicates.

[session] Ensure access to rql varmaker always mark the session as dirty When one accesses the rql_varmaker, that's usually to use it. The pb was that when the varmaker was already in page's data (which is stored as session data), session storage such as redis won't see that the session data is dirty and has to be stored back at the end of the request. To fix this, systematically call set_page_data.

typo

[native] Use cnx.system_sql instead of doexec method in syntax_tree_search The latter handles connection issues and tries to reconnect. Method syntax_tree_search appears to be called from quite a few place where it seems useful to be resilient to connection issues (authentication for instance). This reconnection logic appears to have disappeared at some point when working on https://www.cubicweb.org/2919309. Could not find the exact reason though...

Remove usage of cnx.ensure_cnx_set context manager It has been deprecated since 3.21, no reason to keep using it internally.

[hooks/test/synschema] remove an unneeded skipTest. Related to #5557633.