Fix attachment backfill mock tests

ts/test-mock/bootstrap.ts

@@ -34,6 +34,7 @@ import {
   encryptAttachmentV2,
   generateAttachmentKeys,
 } from '../AttachmentCrypto.js';
+import { isVideoTypeSupported } from '../util/GoogleChrome.js';
 
 export { App };
 
@@ -689,7 +690,7 @@ export class Bootstrap {
         plaintext: {
           data,
         },
-        needIncrementalMac: true,
+        needIncrementalMac: isVideoTypeSupported(contentType),
         sink: passthrough,
       }),
       this.server.storeAttachmentOnCdn(cdnNumber, cdnKey, passthrough),

ts/test-mock/messaging/backfill_test.ts

@@ -197,6 +197,7 @@ describe('attachment backfill', function (this: Mocha.Suite) {
       .getByRole('button', {
         name: 'Open this attachment in a larger view',
       })
+      .first()
       .waitFor();
 
     debug('failing second attachment');