fix np.loadtxt DeprecationWarning

[njzjz]

DeprecationWarning: loadtxt(): Parsing an integer via a float is deprecated.  To avoid this warning, you can:
    * make sure the original data is stored as integers.
    * use the `converters=` keyword argument.  If you only use
      NumPy 1.23 or later, `converters=float` will normally work.
    * Use `np.loadtxt(...).astype(np.int64)` parsing the file as
      floating point and then convert it.  (On all NumPy versions.)
  (Deprecated NumPy 1.23)
  return np.loadtxt(str(self.path), **kwargs)

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (6e306fa) 79.37% compared to head (e1280c4) 79.38%.

Additional details and impacted files

@@           Coverage Diff           @@
##            devel    #2802   +/-   ##
=======================================
  Coverage   79.37%   79.38%           
=======================================
  Files         244      244           
  Lines       25875    25875           
  Branches     1533     1533           
=======================================
+ Hits        20539    20541    +2     
  Misses       4937     4937           
+ Partials      399      397    -2     

Files Changed	Coverage Δ
deepmd/utils/data.py	93.81% <100.00%> (ø)

... and 1 file with indirect coverage changes

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