Update PyTorch to 1.9.1 in CI

[zhiqwang]

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[codecov]

Codecov Report

Merging #181 (2ca04a5) into master (06022fd) will not change coverage.
The diff coverage is n/a.

❗ Current head 2ca04a5 differs from pull request most recent head 138ad1d. Consider uploading reports for the commit 138ad1d to get more accurate results

@@           Coverage Diff           @@
##           master     #181   +/-   ##
=======================================
  Coverage   96.17%   96.17%           
=======================================
  Files          10       10           
  Lines         601      601           
=======================================
  Hits          578      578           
  Misses         23       23           

Flag	Coverage Δ
unittests	96.17% <ø> (ø)

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