[Cherry-pick for 0.18] Update the download url in class EMNIST #8350 (#8365)

Co-authored-by: JavaZero <71128095+JavaZeroo@users.noreply.github.com>

Author: NicolasHug

torchvision/datasets/mnist.py

@@ -276,7 +276,7 @@ class EMNIST(MNIST):
             target and transforms it.
     """
 
-    url = "https://www.itl.nist.gov/iaui/vip/cs_links/EMNIST/gzip.zip"
+    url = "https://biometrics.nist.gov/cs_links/EMNIST/gzip.zip"
     md5 = "58c8d27c78d21e728a6bc7b3cc06412e"
     splits = ("byclass", "bymerge", "balanced", "letters", "digits", "mnist")
     # Merged Classes assumes Same structure for both uppercase and lowercase version