Use schema from bids-standard/bids-specification#1884

.github/workflows/validate_datasets.yml

@@ -111,4 +111,4 @@ jobs:
       env:
         # When proposing new features, schema changes may be necessary.
         # Update this URL to the schema.json from PRs to the spec, when needed.
-        BIDS_SCHEMA: https://bids-specification.readthedocs.io/en/latest/schema.json
+        BIDS_SCHEMA: https://bids-specification--1884.org.readthedocs.build/en/1884/schema.json