Fix `ViTMSNForImageClassification` doctest
# What does this PR do?

`>>> torch.manual_seed`  requires `# doctest: +IGNORE_RESULT`, otherwise we get 

```
Expected nothing
Got:
    <torch._C.Generator object at 0x7fe914fdbcd0>
```
I missed this detail when reviewing #19183

Confirmed it works now (on GCP CPU VM)
_The documentation is not available anymore as the PR was closed or merged._