GitHub changed which keys are supported in SSH and removed the unencrypted Git protocol.
You can read more about the motivation behind these changes in our blog post from last September.
As a reminder, these changes were:

  • Removed all support for DSA keys
  • Required SHA-2 signatures on all RSA keys uploaded after November 2, 2021 (RSA keys uploaded prior to the cutoff may still use SHA-1 signatures)
  • Removed legacy SSH algorithms HMAC-SHA-1 and CBC ciphers
  • Permanently disabled the unencrypted Git protocol