* SQL increase length of VARCHAR fields
Increase length of all fields, keeping the limits for:
* Unique indexes on UTF-8: 191 bytes for MySQL;
* Unique indexes on ASCII: 767 bytes for MySQL;
* Max URL for external tools: 32768 characters;
* Max VARCHAR: 65535 bytes for MySQL;
Follow-up of https://github.com/FreshRSS/FreshRSS/pull/5038
Fix https://github.com/FreshRSS/FreshRSS/issues/4986
* Fix length test