fix(vanta): declare the removed uploadMimeType subblock as dropped

check-block-registry fails a PR that deletes a subblock id without a
migration entry, because a deployed workflow can still hold a value under
that id. The serializer already discards an orphan silently, but the repo's
contract is that the removal is declared rather than inferred.

Uses the _removed_ form, scoped to upload_document_file: the value has no
replacement field to move to.

Author: waleedlatif1

apps/sim/lib/workflows/migrations/subblock-migrations.ts

@@ -292,6 +292,19 @@ export const SUBBLOCK_ID_MIGRATIONS: Record<string, readonly SubblockIdMigration
    * dropped outright.
    */
   sap_concur: [{ from: 'forwardId', to: '_removed_forwardId' }],
+  /**
+   * `uploadMimeType` was an advanced MIME Type input on Upload Document File whose
+   * value the upload path never read: the content type is resolved from storage and
+   * that resolution is never empty, so the field's value lost the `||` chain every
+   * time. Dropped rather than renamed — there is no field for the value to move to.
+   */
+  vanta: [
+    {
+      from: 'uploadMimeType',
+      to: '_removed_uploadMimeType',
+      whenOperation: ['upload_document_file'],
+    },
+  ],
 }
 
 /** Reads the value out of a stored subblock entry, tolerating a bare value. */