clone pytorch.github.io with depth 1 (#48115)
Summary:
Speeds up clone of pytorch.github.io in CI/CD - currently takes ~7 minutes each run.
Locally these are the results: 3.73 seconds vs 611.87 seconds.
With depth 1:
```
$ time git clone https://github.com/pytorch/pytorch.github.io -b site --depth 1
...
3.73s user 2.97s system 23% cpu 28.679 total
```
Without:
```
$ time git clone https://github.com/pytorch/pytorch.github.io -b site
...
611.87s user 66.16s system 96% cpu 11:41.99 total
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/48115
Reviewed By: mrshenli
Differential Revision: D25107867
Pulled By: ranman
fbshipit-source-id: b6131b51df53b7f71d9b4905181182699c0c6c09
