8231262: Suppress warnings on non-serializable instance fields in security libs serializable classes

Reviewed-by: mullan, chegar

src/java.base/share/classes/javax/security/auth/PrivateCredentialPermission.java

@@ -119,6 +119,7 @@ public final class PrivateCredentialPermission extends Permission {
      *          The set contains elements of type,
      *          {@code PrivateCredentialPermission.CredOwner}.
      */
+    @SuppressWarnings("serial") // Not statically typed as Serializable
     private Set<Principal> principals;  // ignored - kept around for compatibility
     private transient CredOwner[] credOwners;