Update supported Oracle Database

Only mark as supported the version also supported by Oracle

Signed-off-by: Carl Schwan <carl@carlschwan.eu>

Author: CarlSchwan

admin_manual/installation/system_requirements.rst

@@ -25,7 +25,7 @@ For best performance, stability and functionality we have documented some recomm
 |                  | - Alpine Linux                                                        |
 +------------------+-----------------------------------------------------------------------+
 | Database         | - MySQL 8.0 / **8.4** or MariaDB 10.6/ **10.11** (recommended) / 11.4 |
-|                  | - Oracle Database 11g, 18, 21, 23                                     |
+|                  | - Oracle Database 19c, 21c, 23ai                                     |
 |                  |   (*only as part of an enterprise subscription*)                      |
 |                  | - PostgreSQL 13/14/15/16/17                                           |
 |                  | - SQLite 3.24+ (*only recommended for testing and minimal-instances*) |