Context tracking causes issues with SQL that has % and no arguments

[wesleykendall]

Recent changes to pghistory's context tracking ensures %s is used when rendering SQL to inject variables.

This, however, causes issues for SQL with % that doesn't have any arguments. For example, pghistory's context tracking function:

CREATE OR REPLACE FUNCTION _pgh_attach_context()
                RETURNS {cls._meta.db_table}.id%TYPE AS $$
                    DECLARE
...

It's likely best we solve this by using mogrify to render the SQL instead of passing down arguments as %s to Psycopg. This would likely simplify codepaths that have to account for positional/kwarg variable syntax.