Allow metadata updates on meta bucket even in WORM mode (#8657)

This ensures that we can update the

- .minio.sys is updated for accounting/data usage purposes
- .minio.sys is updated to indicate if backend is encrypted
  or not.

cmd/fs-v1-multipart.go

@@ -683,7 +683,7 @@ func (fs *FSObjects) CompleteMultipartUpload(ctx context.Context, bucket string,
 	}
 
 	// Deny if WORM is enabled
-	if globalWORMEnabled {
+	if _, ok := isWORMEnabled(bucket); ok {
 		if _, err := fsStatFile(ctx, pathJoin(fs.fsPath, bucket, object)); err == nil {
 			return ObjectInfo{}, ObjectAlreadyExists{Bucket: bucket, Object: object}
 		}