[BUGFIX] Allow setting SYS/session in ConfigurationManager

The config path SYS/session is similar to SYS/caching/cacheConfigurations.
Within the session configuration path session backends can be set
since TYPO3 8.7.

Allow this path for setting values with the ConfigurationManager.

Resolves: #84536
Releases: master, 8.7
Change-Id: I52649673a16937119136d2fbdd0aa93c924d8f31
Reviewed-on: https://review.typo3.org/56950
Reviewed-by: Helmut Hummel <typo3@helhum.io>
Tested-by: Helmut Hummel <typo3@helhum.io>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>

typo3/sysext/core/Classes/Configuration/ConfigurationManager.php

@@ -76,6 +76,7 @@ class ConfigurationManager
         'EXTCONF',
         'DB',
         'SYS/caching/cacheConfigurations',
+        'SYS/session',
     ];
 
     /**