[DOC] - Update GPU env building page

[kcpevey]

Preliminary Checks

• This issue is not a question, feature request, RFC, or anything other than a bug report. Please post those things in GitHub Discussions: https://github.com/nebari-dev/nebari/discussions

Summary

We need to remove the pytorch channel from the GPU environment instructions. Meta is deprecating that channel - 2.5 is the last release to be pushed there. nightlies stopped already and the 2.6 release will be wheels only.

https://www.nebari.dev/docs/how-tos/use-gpus#2-creating-environments

Related: pytorch/pytorch#138506

Steps to Resolve this Issue

1.Edit the page to exclude the pytorch channel