[Security] Fix OidcUser::eraseCredentials() signature

Author: nicolas-grekas

User/OidcUser.php

@@ -73,7 +73,7 @@ public function getUserIdentifier(): string
         return (string) ($this->userIdentifier ?? $this->getSub());
     }
 
-    public function eraseCredentials()
+    public function eraseCredentials(): void
     {
     }