add back old pytorch_lightning imports

[dberenbaum]

Fixes #625

[codecov-commenter]

Codecov Report

Patch coverage has no change and project coverage change: -0.15 ⚠️

Comparison is base (28a0224) 89.69% compared to head (269c4b2) 89.54%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #627      +/-   ##
==========================================
- Coverage   89.69%   89.54%   -0.15%     
==========================================
  Files          43       43              
  Lines        2988     2993       +5     
  Branches      250      250              
==========================================
  Hits         2680     2680              
- Misses        269      274       +5     
  Partials       39       39              

Impacted Files	Coverage Δ
src/dvclive/lightning.py	0.00% <0.00%> (ø)

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