Export to excel fails with `GDAL Error (1): File extension should be XLSX` when file exists.

```
INSTALL spatial;
LOAD spatial;

create table tbl (x varchar(200));
insert into tbl values('hallo');
-- straight from the docs
COPY tbl TO 'output.xlsx' WITH (FORMAT GDAL, DRIVER 'xlsx');
```

>  Error: IO Error: GDAL Error (1): File extension should be XLSX

```
duckdb -version
v0.9.2 3c695d7ba9

macOS, 14.1.1 (23B81), m1
```