Fix an4 URL

[pyf98]

Hi, this PR adds a backup URL for AN4.

If the original website doesn't respond, the following URL should work:

wget https://huggingface.co/datasets/espnet/an4/resolve/main/an4_sphere.tar.gz

[codecov]

Codecov Report

Merging #4427 (dd42517) into master (301b929) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #4427   +/-   ##
=======================================
  Coverage   82.56%   82.56%           
=======================================
  Files         469      469           
  Lines       40212    40212           
=======================================
  Hits        33203    33203           
  Misses       7009     7009           

Flag	Coverage Δ
test_integration_espnet1	66.58% <ø> (ø)
test_integration_espnet2	49.55% <ø> (ø)
test_python	69.36% <ø> (ø)
test_utils	23.45% <ø> (ø)

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[sw005320]

Thanks, @pyf98!