Changed a ValueError in h_abstraciton heuristics into a warning

[alongd]

ARC shouldn't crush if a single TS cannot be found using heuristics. Converted an error into a logger warning.

[codecov[bot]]

Codecov Report

Merging #649 (5ea0d4d) into main (28c74ea) will increase coverage by 0.01%. The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main     #649      +/-   ##
==========================================
+ Coverage   73.12%   73.13%   +0.01%     
==========================================
  Files          99       99              
  Lines       26283    26283              
  Branches     5497     5496       -1     
==========================================
+ Hits        19220    19223       +3     
+ Misses       5700     5699       -1     
+ Partials     1363     1361       -2     

Impacted Files	Coverage Δ
arc/job/adapters/ts/heuristics.py	82.60% <0.00%> (+0.28%)	:arrow_up:

... and 1 file with indirect coverage changes

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