Fixed a bug in dpgen/auto_test/Lammps.py

[tuoping]

Typo in auto_test/Lammps.pu
The bug is reported here:
https://gitee.com/deepmodeling/deepmd-kit/issues/I3T98B

[codecov-commenter]

Codecov Report

Merging #423 (47645a5) into master (fb08b80) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #423   +/-   ##
=======================================
  Coverage   32.42%   32.42%           
=======================================
  Files          85       85           
  Lines       14346    14346           
=======================================
  Hits         4652     4652           
  Misses       9694     9694           

Impacted Files	Coverage Δ
dpgen/auto_test/Lammps.py	30.94% <100.00%> (ø)

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