workaround for etag issue

Author: mofterdinger

db/common.cds

@@ -1,4 +1,5 @@
 namespace my.bookshop;
+using {sap.attachments.Attachments} from `com.sap.cds/cds-feature-attachments`;
 
 ////////////////////////////////////////////////////////////////////////////
 //
@@ -8,3 +9,7 @@ type TechnicalBooleanFlag : Boolean @(
     UI.Hidden,
     Core.Computed
 );
+
+annotate Attachments with {
+    modifiedAt @(odata.etag: null);
+}