We have special handling for double nots to "pull up" the filter
clauses for greater efficiency. That handling didn't work right
when an `anyOf` was under the double `not`, and we got a `TypeError`:

```
TypeError: no implicit conversion of Integer into Array
  from elastic_graph/graphql/filtering/filter_interpreter.rb:121:in `concat'
  from elastic_graph/graphql/filtering/filter_interpreter.rb:121:in `block (2 levels) in process_not_expression'
  from elastic_graph/graphql/filtering/filter_interpreter.rb:121:in `each'
  from elastic_graph/graphql/filtering/filter_interpreter.rb:121:in `block in process_not_expression'
  from elastic_graph/graphql/filtering/filter_interpreter.rb:120:in `each'
  from elastic_graph/graphql/filtering/filter_interpreter.rb:120:in `process_not_expression'
  from elastic_graph/graphql/filtering/filter_interpreter.rb:66:in `block in process_filter_hash'
  from elastic_graph/graphql/filtering/filter_interpreter.rb:61:in `each'
  from elastic_graph/graphql/filtering/filter_interpreter.rb:61:in `process_filter_hash'
  from elastic_graph/graphql/filtering/filter_interpreter.rb:43:in `block (2 levels) in build_query'
  from set.rb:511:in `each_key'
  from set.rb:511:in `each'
  from elastic_graph/graphql/filtering/filter_interpreter.rb:42:in `block in build_query'
  from <internal:kernel>:90:in `tap'
  from elastic_graph/graphql/filtering/filter_interpreter.rb:337:in `build_bool_hash'
  from elastic_graph/graphql/filtering/filter_interpreter.rb:41:in `build_query'
  from elastic_graph/graphql/datastore_query.rb:318:in `to_datastore_body'
  from elastic_graph/graphql/datastore_query.rb:229:in `empty?'
  from elastic_graph/graphql/datastore_query.rb:94:in `each'
  from elastic_graph/graphql/datastore_query.rb:94:in `partition'
  from elastic_graph/graphql/datastore_query.rb:94:in `perform'
  from elastic_graph/graphql/datastore_search_router.rb:34:in `msearch'
  from elastic_graph/graphql/resolvers/query_source.rb:26:in `fetch'
  from graphql/dataloader/source.rb:136:in `run_pending_keys'
  from graphql/dataloader.rb:294:in `block (2 levels) in spawn_source_fiber'
  from graphql/dataloader.rb:292:in `each'
  from graphql/dataloader.rb:292:in `block in spawn_source_fiber'
  from graphql/dataloader.rb:245:in `block in spawn_fiber'
```

This fixes that case.