Fix pixi tasks for different environments

[melissawm]

References and relevant issues

Follow-up to #900

Description

After we merged #900, I can't build the docs locally with pixi. No tasks are shown when I run

➜  napari-docs git:(main) pixi task list
Tasks that can run on this machine:
-----------------------------------

Task  Description
➜  napari-docs git:(main) 

which means pixi doesn't see any of the tasks defined in our pixi.toml file. Doing some research on the docs, it looks like removing the no-default-feature = true option from the environment solves it. Another option is to list each task again for each of the two environments, but I believe this PR is the simplest fix.

[Czaki]

Yes.

[melissawm]

Thanks!