Add get_fname helper function for GraphGym

[JiaxuanYou]

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[codecov-commenter]

Codecov Report

Merging #3659 (046ba90) into master (560df33) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #3659   +/-   ##
=======================================
  Coverage   81.58%   81.59%           
=======================================
  Files         295      295           
  Lines       14861    14860    -1     
=======================================
  Hits        12125    12125           
+ Misses       2736     2735    -1     

Impacted Files	Coverage Δ
torch_geometric/graphgym/__init__.py	100.00% <100.00%> (ø)
torch_geometric/graphgym/config.py	95.32% <100.00%> (+0.55%)	⬆️

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