Thanks_Tom RR

Is there some nearby lower ground you could drain it to?

1- you could pour a narrow bit of sloped concrete formed in a trough to drain the water to a better place.

2- might be a pain but you could bury a perforated pipe (French tile) covered with pea gravel and route it even further away.

3- if the water is coming from the garden plot, you could line that bottom/end with plastic sheet to prevent the water from escaping the side by the shed.

If it’s solely from rain water from above, you could have a metal flashing made to cover the gap between the shed and garden. Mount the high side on the shed and let it run into the garden.