[BUG] Self-concat breaks with the RayRunner

[jaychia]

Problem: when performing a dataframe concat with itself, our RayRunner will break on a .wait() call which waits on some duplicate object IDs

[codecov]

Codecov Report

Merging #1617 (7267527) into main (c4b498a) will increase coverage by 0.00%.
Report is 2 commits behind head on main.
The diff coverage is 100.00%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1617   +/-   ##
=======================================
  Coverage   84.59%   84.60%           
=======================================
  Files          54       54           
  Lines        5201     5202    +1     
=======================================
+ Hits         4400     4401    +1     
  Misses        801      801           

Files	Coverage Δ
daft/runners/ray_runner.py	89.82% <100.00%> (+0.02%)	⬆️

... and 1 file with indirect coverage changes