Fix dead links to Tensorboard (#6075)

Ignore spurious dead links to tensorflow.org pages, since we're seeing an infinite redirect for some reason that doesn't reproduce in the browser or with `curl`.

docs/Background-PyTorch.md

@@ -24,7 +24,7 @@ One component of training models with PyTorch is setting the values of
 certain model attributes (called _hyperparameters_). Finding the right values of
 these hyperparameters can require a few iterations. Consequently, we leverage a
 visualization tool called
-[TensorBoard](https://www.tensorflow.org/programmers_guide/summaries_and_tensorboard).
+[TensorBoard](https://www.tensorflow.org/tensorboard).
 It allows the visualization of certain agent attributes (e.g. reward) throughout
 training which can be helpful in both building intuitions for the different
 hyperparameters and setting the optimal values for your Unity environment. We

docs/Using-Tensorboard.md

@@ -2,7 +2,7 @@
 
 The ML-Agents Toolkit saves statistics during learning session that you can view
 with a TensorFlow utility named,
-[TensorBoard](https://www.tensorflow.org/programmers_guide/summaries_and_tensorboard).
+[TensorBoard](https://www.tensorflow.org/tensorboard).
 
 The `mlagents-learn` command saves training statistics to a folder named
 `results`, organized by the `run-id` value you assign to a training session.

markdown-link-check.full.json

@@ -23,6 +23,10 @@
         {
             "pattern": "https://www.researchgate.net/",
             "comment": "Issue with GHE certs / firewall"
+        },
+        {
+            "pattern": "https://www.tensorflow.org/",
+            "comment": "Valid links failing with errors like 'https://www.tensorflow.org/tensorboard → Status: 0 Error: Exceeded maxRedirects. Probably stuck in a redirect loop'"
         }
     ]
 }