Hard to see so I can't say for sure just by looking at a photograph. But, there is 99% chance that is is a layer of skin that grew on the cotyledons while the seed was developing. It grows on them as a protection to help slow down the parts of the seed from drying out.
When the seed was germinating or sprouting (both words have the same basic meaning) the two cotyledons pull apart as they break through the surface of the soil. As they pull apart sometimes that layer of skin will start to pull off from the cotyledon. It has never been a problem that I have noticed. By the way, it is easy to see if a gardener is growing something with larger sized seeds -- something like beans. The smaller the seed the harder it is to see.
Or, figure out a way to raise and lower the plant. Put the plant on an upside down bucket while it is small and as it grows taller take the bucket out and use a smaller bucket.
The only thing is that you will have to drill holes in the bottom to let water drain out.
Just my thoughts but once you drill the holes the dishpan or whatever that container is will be ruined for just about any other use. Best to get a proper plant pot of 10 or 12 liter size, or maybe even larger, with the holes already cut into the bottom.
Kind of like when someone has a 15 meter length of rope. Once they start cutting it they have pieces of rope and when they need to do something with a long piece of rope they will have to go out and buy another 15 meter length. Save the pan for when you might actually need it for something, maybe to hold water for mixing up some liquid fertilizer.