system_update_6015 does not use global collation when creating table cache_form

system_update_6015 directly creates the {cache_form} table using an update_sql($query) call rather than via the standard db_create_table() function (which would indirectly pick up the globally set $db_collation value if it has been defined).

I don't know if there is a good reason why that table is directly created using update_sql() rather than by the Drupal standard table creation routine but it seems to be the only instance of this in the system. The upshot is that that table is created with the default connection collation (in my case utf8_general_ci) instead of the desired specific collation (for me utf8_unicode_ci).

Reproducable by running that system update step with $db_collation in settings.php set to something other than your default connection collation.