The validation for setViewport says:

If any of the following conditions are unsatisfied, make this invalid and stop.
...
minDepth < maxDepth

However, based on the discussion in gpuweb/cts#3307 (comment):

This seems like a bug in the WebGPU spec. I can't exactly recall exactly the discussions around this, but it seems the only constraint was reverse depth, not < vs <=. The D3D11 functional spec require <=, not < and that's the only constraint I have found (Vulkan doesn't have a constraint even in 1.0, and Metal docs say the two can be reversed).

it seems like that line should read:

minDepth <= maxDepth