Disable multiprocessing dataloader in tensorboard tutorial and ignore tensorboard deprecation warning (#3550)

## Description
This PR disables the multiprocessing dataloader in the tensorboard
tutorial because enabling the multiprocessing dataloader (num_workers=2)
caused a runtime error when running the tutorial code on mac.

This PR also ignores a deprecation warning from tensorboard as
tensorboard isn't actively fixing it
(tensorflow/tensorboard#7003).

## Checklist
<!--- Make sure to add `x` to all items in the following checklist: -->
- [ ] The issue that is being fixed is referred in the description (see
above "Fixes #ISSUE_NUMBER")
- [ ] Only one issue is addressed in this pull request
- [ ] Labels from the issue that this PR is fixing are added to this
pull request
- [ ] No unnecessary issues are included into this pull request.

---------

Co-authored-by: sekyondaMeta <[email protected]>

Author: jiannanWang

intermediate_source/tensorboard_tutorial.rst

@@ -60,12 +60,9 @@ We'll begin with similar boilerplate code as in the `CIFAR-10 tutorial <https://
         transform=transform)
 
     # dataloaders
-    trainloader = torch.utils.data.DataLoader(trainset, batch_size=4,
-                                            shuffle=True, num_workers=2)
+    trainloader = torch.utils.data.DataLoader(trainset, batch_size=4, shuffle=True)
 
-
-    testloader = torch.utils.data.DataLoader(testset, batch_size=4,
-                                            shuffle=False, num_workers=2)
+    testloader = torch.utils.data.DataLoader(testset, batch_size=4, shuffle=False)
 
     # constant for classes
     classes = ('T-shirt/top', 'Trouser', 'Pullover', 'Dress', 'Coat',
@@ -159,7 +156,7 @@ Now running
 
 ::
 
-    tensorboard --logdir=runs
+    PYTHONWARNINGS="ignore:pkg_resources is deprecated as an API:UserWarning" tensorboard --logdir=runs
 
 from the command line and then navigating to `http://localhost:6006 <http://localhost:6006>`_
 should show the following.