`kart export` fails on datasets where geometry type is `GEOMETRY Z`

For example: `kart export dataset_with_z /tmp/dataset_with_z.fgb --crs=EPSG:4326` Crashes with ``` kart helper: unhandled exception Traceback (most recent call last): File "kart/helper.py", line 240, in helper File "click/core.py", line 1157, in __call__ File "click/core.py", line 1078, in main File "kart/cli_util.py", line 72, in invoke File "click/core.py", line 1688, in invoke File "click/core.py", line 1434, in invoke File "click/core.py", line 783, in invoke File "click/decorators.py", line 33, in new_func File "kart/export.py", line 40, in export File "kart/cli_util.py", line 454, in forward_context_to_command File "click/core.py", line 804, in forward File "click/core.py", line 783, in invoke File "click/decorators.py", line 33, in new_func File "kart/tabular/export.py", line 244, in table_export KeyError: 'GEOMETRY Z' ``` **Expected behaviour** Should export as normal. **Version Info ** Kart v0.16.2.dev0+ci.6460.gite9b7a55a