fix(sdmx_series_ecb_bkn): refresh content digest after key strip

sdmx_series_ecb_bkn/meta.json

@@ -45,8 +45,8 @@
   "build": {
     "built_at": "2026-06-18T22:28:49.842278Z",
     "parsimony_version": null,
-    "builder": null,
-    "content_sha256": "103faad9d5dab2fdcd35511ee071dfa44d0b852097f0c2409a3bdd27ce56d8db",
+    "builder": "strip-ecb-flow-prefix-keys",
+    "content_sha256": "55e00ca50644dbbda495e60d519c3e590496030a7e4ecd92444954c3fd0c0513",
     "manifest_contract_sha256": "1c211d9847a227b77e4d950aa0807fa0103b47d86fe7f0858322996526fa5dbb"
   }
 }