refactor(security): replace generic event with severity enum

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

core/lib/Security/Event/FirewallSettingsUpdatedEvent.php

@@ -69,8 +69,8 @@ final class FirewallSettingsUpdatedEvent extends Event implements SecurityEventI
         return $this->changeReason;
     }
 
-    public function getSeverity(): int
+    public function getSeverity(): SecurityEventSeverity
     {
-        return SecurityEvent::SEVERITY_INFO;
+        return SecurityEventSeverity::INFO;
     }
 }