refactor(security): replace generic event with severity enum

Signed-off-by: Sebastian Krupinski <krupinski01@gmail.com>

core/lib/Security/Event/FirewallRuleEvent.php

@@ -151,8 +151,8 @@ abstract class FirewallRuleEvent extends Event implements SecurityEventInterface
         return $this->reason;
     }
 
-    public function getSeverity(): int
+    public function getSeverity(): SecurityEventSeverity
     {
-        return SecurityEvent::SEVERITY_INFO;
+        return SecurityEventSeverity::INFO;
     }
 }