Fix CI build with conda-forge::pytorch (#162)

Summary:
The CI build for Ubuntu with GPU enabled is [failing](https://github.com/facebookincubator/momentum/actions/runs/12207717521/job/34059648061?fbclid=IwZXh0bgNhZW0CMTEAAR3rvQlZa-R1hsCPZz2hy1OcGE523aAXwsDLzdA3VDWdeok81IbAqtvgYWM_aem_dmhm3556lPnQvLItjH6A3w) due to the latest conda-forge::pytorch build being broken. Now that it's [fixed](conda-forge/pytorch-cpu-feedstock#300), this PR resolves the CI failure by updating the pixi lock file to use the fixed pytorch build.

## Checklist:

- [x] Adheres to the [style guidelines](https://facebookincubator.github.io/momentum/docs/developer_guide/style_guide)
- [x] Codebase formatted by running `pixi run lint`

Pull Request resolved: #162

Test Plan:
Run the following on Ubuntu:
```
pixi update && pixi upgrade
pixi run -e gpu test_py
```

Reviewed By: juliencbmeta

Differential Revision: D66939558

Pulled By: jeongseok-meta

fbshipit-source-id: 940b5488824e26300c17a04ecb03d8833bcd0483