docs(admin): list Redis 4.0+ in system requirements

Assisted-by: Cursor:grok-4.7
Signed-off-by: whoalin1 <whoalin414@gmail.com>

Author: whoalin1

admin_manual/installation/system_requirements.rst

@@ -39,6 +39,11 @@ For best performance, stability and functionality we have documented some recomm
 |                  | - 8.4                                                                 |
 |                  | - **8.5** (*recommended*)                                             |
 +------------------+-----------------------------------------------------------------------+
+| Cache / locking  | - **Redis** Open Source **4.0+** (recommended for distributed cache   |
+| (optional)       |   and file locking; see :doc:`../configuration_server/caching_configuration`) |
+|                  | - Valkey / KeyDB (Redis-compatible; expected to work)                 |
+|                  | - APCu for local memory cache                                         |
++------------------+-----------------------------------------------------------------------+
 
 See :doc:`source_installation` for minimum PHP-modules and additional software for installing Nextcloud.