Enable parallel training UT in GitHub CI.

[shishaochen]

With the latest TensorFlow package, enable parallel training unit test.

[codecov-commenter]

Codecov Report

Merging #1075 (9c2b35c) into devel (75160c7) will decrease coverage by 10.90%.
The diff coverage is n/a.

❗ Current head 9c2b35c differs from pull request most recent head 4280000. Consider uploading reports for the commit 4280000 to get more accurate results

@@             Coverage Diff             @@
##            devel    #1075       +/-   ##
===========================================
- Coverage   75.19%   64.28%   -10.91%     
===========================================
  Files          82        5       -77     
  Lines        6945       14     -6931     
===========================================
- Hits         5222        9     -5213     
+ Misses       1723        5     -1718     

Impacted Files	Coverage Δ
deepmd/calculator.py
deepmd/infer/deep_pot.py
deepmd/cluster/slurm.py
deepmd/utils/sess.py
source/op/_soft_min_force_grad.py
deepmd/loss/__init__.py
deepmd/infer/data_modifier.py
source/op/_gelu.py
deepmd/utils/convert.py
deepmd/utils/weight_avg.py
... and 76 more

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