MFH: r568541

databases/postgresql-mysql_fdw: Upgrade from 2.5.4 to 2.5.5

Fix various bugs, compilation warnings, and server crashes.
Souce: https://github.com/EnterpriseDB/mysql_fdw/releases/tag/REL-2_5_5

Also make minimum PostgreSQL version 9.6. The last version 2.5.4 already
dropped the PostgreSQL 9.5 support. Also imcrease max supported PostgreSQL
version from 11 to 13. This was also introduced in the last version 2.5.4.

Take maintainership

Sponsored by: Bounce Experts

M postgresql-mysql_fdw/Makefile
M postgresql-mysql_fdw/distinfo