Tests failing hard on MacOS

New sha512 hash thing fails on MacOS. crypt(3) on MacOS is quite legacy and only implements DES. We fixed this for an older test in e9c075d0

  * test checkpw/2 check sha512-crypt hash (0.6ms)

  1) test checkpw/2 check sha512-crypt hash (Pleroma.Plugs.AuthenticationPlugTest)
     test/plugs/authentication_plug_test.exs:67
     Expected truthy, got false
     code: assert AuthenticationPlug.checkpw("password", hash)
     arguments:

         # 1
         "password"

         # 2
         "$6$9psBWV8gxkGOZWBz$PmfCycChoxeJ3GgGzwvhlgacb9mUoZ.KUXNCssekER4SJ7bOK53uXrHNb2e4i8yPFgSKyzaW9CcmrDXWIEMtD1"

     stacktrace:
       test/plugs/authentication_plug_test.exs:71: (test)