fix info not pass issue in PGPolicy

[Trinkle23897]

close #775

[codecov-commenter]

Codecov Report

Merging #787 (04ce489) into master (4c3791a) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #787      +/-   ##
==========================================
+ Coverage   91.07%   91.09%   +0.01%     
==========================================
  Files          71       73       +2     
  Lines        5077     5088      +11     
==========================================
+ Hits         4624     4635      +11     
  Misses        453      453              

Flag	Coverage Δ
unittests	91.09% <100.00%> (+0.01%)	⬆️

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Impacted Files	Coverage Δ
tianshou/__init__.py	100.00% <100.00%> (ø)
tianshou/policy/modelfree/pg.py	100.00% <100.00%> (ø)
tianshou/utils/__init__.py	100.00% <0.00%> (ø)

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