org.openmrs.api.APIException: Editing some fields on Obs is not allowed

@dkayiwa for some reason, this stopped working(I think it used to work before). Here’s this solution implemented here https://github.com/openmrs/openmrs-module-attachments/blob/master/omod-2.0/src/main/java/org/openmrs/module/attachments/rest/AttachmentResource2_0.java#L17-L18.

This test https://github.com/openmrs/openmrs-module-attachments/blob/master/omod-2.0/src/test/java/org/openmrs/module/attachments/rest/AttachmentRestController2_0Test.java#L98-L108 passes but the error is thrown at runtime on platform 2.3.0 and 2.1.x.