Fix update of weather_forecast

The real problem was that i was trying to update the forecast via
pgx.Pool, not the acquired connection, therefore it did not have the
correct role.

I moved everything to a different function where db is not visible in
scope, just to make sure i did not fuck up anywhere else.

cmd/camper-weather/main.go

@@ -42,13 +42,16 @@ func main() {
 		log.Fatal(err)
 	}
 	defer conn.Release()
+	updateForecast(context.Background(), conn)
+}
 
-	if _, err := conn.Exec(context.Background(), "set role to admin"); err != nil {
+func updateForecast(ctx context.Context, conn *database.Conn) {
+	if _, err := conn.Exec(ctx, "set role to admin"); err != nil {
 		log.Fatal(err)
 	}
 
 	var stationURL string
-	if err := conn.QueryRow(context.Background(), `
+	if err := conn.QueryRow(ctx, `
 		select station_uri
 		from weather_forecast
 	`).Scan(
@@ -68,7 +71,7 @@ func main() {
 	}
 
 	for _, forecast := range result.Forecasts {
-		if _, err := db.Exec(context.Background(), `
+		if _, err := conn.Exec(ctx, `
 			update weather_forecast
 			set weather_condition_id = $1
 			  , day_temperature = $2