Schema: Remove collation from blob field

Column defined as mediumblob with COLLATE utf8mb4_unicode_ci, which is the root
cause of the issue. BLOB (Binary Large Object) data types don't support
collations because they are meant to store binary data (i.e., raw bytes), which
is not interpreted as text.

schema/mysql/schema.sql

@@ -1,7 +1,7 @@
 CREATE TABLE annotation (
   uuid binary(16) NOT NULL,
   name varchar(63) COLLATE utf8mb4_unicode_ci NOT NULL,
-  value mediumblob COLLATE utf8mb4_unicode_ci NOT NULL,
+  value mediumblob NOT NULL,
   PRIMARY KEY (uuid)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_bin;