1.2.1 fixes a SQL injection via wrongly escaped bytes parameters on the
big5, gbk, sjis, cp932 and gb18030 charsets (GHSA-x4f8-9hx9-hpp9).
Drop the pymysql.converters assertions from test.sh: escape_dict is now
a non-callable placeholder kept only for aiomysql, and upstream states
the module is internal with no compatibility guarantee.
Signed-off-by: Alexandru Ardelean <alex@shruggie.ro>