Fix: update DimeNet pretrained checkpoint loading for compatibility with Tensorflow v2.X

[nhadler]

No description provided.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.09%. Comparing base (c211214) to head (39afb5d).
⚠️ Report is 142 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #10547      +/-   ##
==========================================
- Coverage   86.11%   85.09%   -1.02%     
==========================================
  Files         496      510      +14     
  Lines       33655    35964    +2309     
==========================================
+ Hits        28981    30604    +1623     
- Misses       4674     5360     +686     

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