Enable Redis session tests back for PHP 7.2 and up

(this is part of https://tracker.moodle.org/browse/MDLSITE-5876)

This reverts commit 2c7756f.

Author: stronk7

config.docker-template.php

@@ -58,11 +58,7 @@
     define('TEST_SEARCH_SOLR_INDEXNAME', 'test');
     define('TEST_SEARCH_SOLR_PORT', 8983);
 
-    // We need to keep Redis session tests disabled for PHP 7.2 and up. See MDL-60978.
-    if (version_compare(PHP_VERSION, '7.2.0', '<')) {
-        define('TEST_SESSION_REDIS_HOST', 'redis');
-    }
-
+    define('TEST_SESSION_REDIS_HOST', 'redis');
     define('TEST_CACHESTORE_REDIS_TESTSERVERS', 'redis');
 
     define('TEST_CACHESTORE_MONGODB_TESTSERVER', 'mongodb://mongo:27017');