docs: code examples running successfully

## Description

This pull request solves both pytorch#72921 and an identical, unreported issue in another part of the documentation.

## Documentation Changes Preview

- ### Typo in https://pytorch.org/docs/stable/generated/torch.no_grad.html#codecell0:

  #### Before:
  ![1-original](https://user-images.githubusercontent.com/59971270/157734766-e15bf0cb-c6d4-4958-82cb-53a8de9fa186.png)

  #### After:
  ![1-corrected](https://user-images.githubusercontent.com/59971270/157734774-570108b8-0b93-4139-817d-02315a6262e3.png)

- ### Typo in https://pytorch.org/docs/stable/generated/torch.autograd.set_grad_enabled.html?highlight=set_grad_enabled#codecell0:

  #### Before:
  ![2-original](https://user-images.githubusercontent.com/59971270/157734859-9185f57b-0767-465e-b683-809be836a947.png)

  #### After:
  ![2-corrected](https://user-images.githubusercontent.com/59971270/157734863-5fa4caee-818a-463d-872b-4231007940f8.png)

Pull Request resolved: pytorch#74044
Approved by: https://github.com/albanD

Author: MattiaSarti

torch/autograd/grad_mode.py

@@ -111,7 +111,7 @@ class no_grad(_DecoratorContextManager):
 
     Example::
 
-        >>> x = torch.tensor([1], requires_grad=True)
+        >>> x = torch.tensor([1.], requires_grad=True)
         >>> with torch.no_grad():
         ...   y = x * 2
         >>> y.requires_grad
@@ -206,7 +206,7 @@ class set_grad_enabled(_DecoratorContextManager):
 
     Example::
 
-        >>> x = torch.tensor([1], requires_grad=True)
+        >>> x = torch.tensor([1.], requires_grad=True)
         >>> is_train = False
         >>> with torch.set_grad_enabled(is_train):
         ...   y = x * 2