copy_from_query drops headers if any postgis NOTICE/LOCATION messages produced

Personne n'a encore pris cette issue.

when using `Connection.copy_from_query` I had a statement which eventually resolved to something like:
```sql
COPY (
select 1
from field_year_crop_variety_layer fycvl
cross join filters
join field_meta fm on
fm.field_id = fycvl.field_id and
(filters.filter_geometry is null or st_intersects(filters.filter_geometry, fm.centroid))
order by fycvl.field_id, fycvl.harvest_year, fycvl.layer_id, fycvl.crop, fycvl.variety
limit '100000'::int
) TO STDOUT (FORMAT 'csv', HEADER True)
```

where `filter_geometry` is a `geometry`, and `fm.centroid` is a `geography`.

and no matter what I did asyncpg would not return the headers. It wasn't until I broke it down and ran it from psql that I noticed the output:
```
field_id,harvest_year,layer_id,crop,variety,is_precision_data,date_period,avg_date,data_is_missing,missing_data_message,crop_variety_layer_area_m2,geometry,computed_at
NOTICE: 00000: Coordinate values were coerced into range [-180 -90, 180 90] for GEOGRAPHY
LOCATION: geography_from_geometry, geography_inout.c:510
NOTICE: 00000: Coordinate values were coerced into range [-180 -90, 180 90] for GEOGRAPHY
LOCATION: geography_from_geometry, geography_inout.c:510
143011,2017,0,corn,unknown,t,"[2017-04-25,2017-04-26)",2017-04-24,f,,7240.833,,1752130305.616610
```

sure enough, if I fixed the bug (casting fm.centroid to a geometry) the headers appeared. This seems like a bug in asyncpg when interpreting the data returned.

Commencez avec Connection.copy_from_query et reproduisez la requête COPY fournie contre PostgreSQL avec les messages NOTICE/LOCATION de PostGIS activés. Suivez la manière dont ces messages sont traités avec la sortie de COPY ; c’est terminé lorsque les données renvoyées conservent leur en-tête CSV lorsque de tels messages sont produits.

Rédigé par le modèle d'indexation à partir du texte de l'issue.